We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.
A method that should be called from every well-designed equals method that is open to be overridden in a subclass.
A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.
the value being probed for possible equality
true if this instance can possibly equal that
, otherwise false
Returns the option's value.
Returns the option's value.
if the option is empty.
The option must be nonEmpty.
Returns true if the option is None
, false otherwise.
The size of this product.
The nth element of this product, 0-based.
The nth element of this product, 0-based. In other words, for a
product A(x1, ..., xk)
, returns x(n+1)
where 0 < n < k
.
the index of the element to return
the element n
elements after the first element
Test two objects for inequality.
Test two objects for inequality.
true
if !(this == that), false otherwise.
Equivalent to x.hashCode
except for boxed numeric types and null
.
Equivalent to x.hashCode
except for boxed numeric types and null
.
For numerics, it returns a hash value which is consistent
with value equality: if two value type instances compare
as true, then ## will produce the same hash value for each
of them.
For null
returns a hashcode where null.hashCode
throws a
NullPointerException
.
a hash value consistent with ==
[use case] Returns a new option containing the elements from the left hand operand followed by the elements from the right hand operand.
Returns a new option containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the option is the most specific superclass encompassing the element types of the two operands.
Example:
scala> val a = LinkedList(1) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1) scala> val b = LinkedList(2) b: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val c = a ++ b c: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2) scala> val d = LinkedList('a') d: scala.collection.mutable.LinkedList[Char] = LinkedList(a) scala> val e = c ++ d e: scala.collection.mutable.LinkedList[AnyVal] = LinkedList(1, 2, a)
the element type of the returned collection.
the traversable to append.
a new option which contains all elements of this option
followed by all elements of that
.
As with ++
, returns a new collection containing the elements from the
left operand followed by the elements from the right operand.
As with ++
, returns a new collection containing the elements from the
left operand followed by the elements from the right operand.
It differs from ++
in that the right operand determines the type of
the resulting collection rather than the left one.
Mnemonic: the COLon is on the side of the new COLlection type.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
This overload exists because: for the implementation of ++:
we should
reuse that of ++
because many collections override it with more
efficient versions.
Since TraversableOnce
has no ++
method, we have to implement that
directly, but Traversable
and down can use the overload.
the element type of the returned collection.
the class of the returned collection. In the standard library configuration, That
is Iterable[B]
the traversable to append.
an implicit value of class CanBuildFrom
which determines the result class That
from the current
representation type Repr
and the new element type B
.
a new collection of type That
which contains all elements
of this option followed by all elements of that
.
[use case] As with ++
, returns a new collection containing the elements from the left operand followed by the
elements from the right operand.
As with ++
, returns a new collection containing the elements from the left operand followed by the
elements from the right operand.
It differs from ++
in that the right operand determines the type of
the resulting collection rather than the left one.
Mnemonic: the COLon is on the side of the new COLlection type.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
the element type of the returned collection.
the traversable to append.
a new option which contains all elements of this option
followed by all elements of that
.
Applies a binary operator to a start value and all elements of this option, going left to right.
Applies a binary operator to a start value and all elements of this option, going left to right.
Note: /:
is alternate syntax for foldLeft
; z /: xs
is the same as
xs foldLeft z
.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = (5 /: a)(_+_) b: Int = 15 scala> val c = (5 /: a)((x,y) => x + y) c: Int = 15
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this option,
going left to right with the start value z
on the left:
op(...op(op(z, x_1), x_2), ..., x_n)
where x1, ..., xn
are the elements of this option.
Applies a binary operator to all elements of this option and a start value, going right to left.
Applies a binary operator to all elements of this option and a start value, going right to left.
Note: :\
is alternate syntax for foldRight
; xs :\ z
is the same as
xs foldRight z
.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = (a :\ 5)(_+_) b: Int = 15 scala> val c = (a :\ 5)((x,y) => x + y) c: Int = 15
the result type of the binary operator.
the start value
the binary operator
the result of inserting op
between consecutive elements of this option,
going right to left with the start value z
on the right:
op(x_1, op(x_2, ... op(x_n, z)...))
where x1, ..., xn
are the elements of this option.
Test two objects for equality.
Test two objects for equality.
The expression x == that
is equivalent to if (x eq null) that eq null else x.equals(that)
.
true
if the receiver object is equivalent to the argument; false
otherwise.
Appends all elements of this option to a string builder.
Appends all elements of this option to a string builder.
The written text consists of the string representations (w.r.t. the method
toString
) of all elements of this option without any separator string.
Example:
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> val h = a.addString(b) b: StringBuilder = 1234
the string builder to which elements are appended.
the string builder b
to which elements were appended.
Appends all elements of this option to a string builder using a separator string.
Appends all elements of this option to a string builder using a separator string.
The written text consists of the string representations (w.r.t. the method toString
)
of all elements of this option, separated by the string sep
.
Example:
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> a.addString(b, ", ") res0: StringBuilder = 1, 2, 3, 4
the string builder to which elements are appended.
the separator string.
the string builder b
to which elements were appended.
Appends all elements of this option to a string builder using start, end, and separator strings.
Appends all elements of this option to a string builder using start, end, and separator strings.
The written text begins with the string start
and ends with the string end
.
Inside, the string representations (w.r.t. the method toString
)
of all elements of this option are separated by the string sep
.
Example:
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> a.addString(b, "LinkedList(", ", ", ")") res1: StringBuilder = LinkedList(1, 2, 3, 4)
the string builder to which elements are appended.
the starting string.
the separator string.
the ending string.
the string builder b
to which elements were appended.
Aggregates the results of applying an operator to subsequent elements.
Aggregates the results of applying an operator to subsequent elements.
This is a more general form of fold
and reduce
. It has similar
semantics, but does not require the result to be a supertype of the
element type. It traverses the elements in different partitions
sequentially, using seqop
to update the result, and then applies
combop
to results from different partitions. The implementation of
this operation may operate on an arbitrary number of collection
partitions, so combop
may be invoked an arbitrary number of times.
For example, one might want to process some elements and then produce
a Set
. In this case, seqop
would process an element and append it
to the list, while combop
would concatenate two lists from different
partitions together. The initial value z
would be an empty set.
pc.aggregate(Set[Int]())(_ += process(_), _ ++ _)
Another example is calculating geometric mean from a collection of doubles (one would typically require big doubles for this).
the type of accumulated results
the initial value for the accumulated result of the partition - this
will typically be the neutral element for the seqop
operator (e.g.
Nil
for list concatenation or 0
for summation)
an operator used to accumulate results within a partition
an associative operator used to combine results from different partitions
Cast the receiver object to be of type T0
.
Cast the receiver object to be of type T0
.
Note that the success of a cast at runtime is modulo Scala's erasure semantics.
Therefore the expression 1.asInstanceOf[String]
will throw a ClassCastException
at
runtime, while the expression List(1).asInstanceOf[List[String]]
will not.
In the latter example, because the type argument is erased as part of compilation it is
not possible to check whether the contents of the list are of the requested type.
the receiver object.
if the receiver object is not an instance of the erasure of type T0
.
Create a copy of the receiver object.
Returns a Some containing the result of
applying pf
to this Option's contained
value, if this option is
nonempty and pf
is defined for that value.
[use case] Builds a new collection by applying a partial function to all elements of this option on which the function is defined.
Builds a new collection by applying a partial function to all elements of this option on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the option.
a new option resulting from applying the given partial function
pf
to each element on which it is defined and collecting the results.
The order of the elements is preserved.
Finds the first element of the option for which the given partial function is defined, and applies the partial function to it.
Finds the first element of the option for which the given partial function is defined, and applies the partial function to it.
the partial function
an option value containing pf applied to the first
value for which it is defined, or None
if none exists.
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
The factory companion object that builds instances of class Option
.
The factory companion object that builds instances of class Option
.
(or its Iterable
superclass where class Option
is not a Seq
.)
[use case] Copies elements of this option to an array.
Copies elements of this option to an array.
Fills the given array xs
with at most len
elements of
this option, starting at position start
.
Copying will stop once either the end of the current option is reached,
or the end of the array is reached, or len
elements have been copied.
the array to fill.
the starting index.
the maximal number of elements to copy.
[use case] Copies values of this option to an array.
Copies values of this option to an array.
Fills the given array xs
with values of this option.
Copying will stop once either the end of the current option is reached,
or the end of the array is reached.
the array to fill.
[use case] Copies values of this option to an array.
Copies values of this option to an array.
Fills the given array xs
with values of this option, beginning at index start
.
Copying will stop once either the end of the current option is reached,
or the end of the array is reached.
the array to fill.
the starting index.
Copies all elements of this option to a buffer.
Copies all elements of this option to a buffer.
The buffer to which elements are copied.
Counts the number of elements in the option which satisfy a predicate.
Counts the number of elements in the option which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p
.
Selects all elements except first n ones.
Selects all elements except first n ones.
the number of elements to drop from this option.
a option consisting of all elements of this option except the first n
ones, or else the
empty option, if this option has less than n
elements.
Selects all elements except last n ones.
Selects all elements except last n ones.
The number of elements to take
a option consisting of all elements of this option except the last n
ones, or else the
empty option, if this option has less than n
elements.
Drops longest prefix of elements that satisfy a predicate.
Drops longest prefix of elements that satisfy a predicate.
the longest suffix of this option whose first element
does not satisfy the predicate p
.
Tests whether the argument (arg0
) is a reference to the receiver object (this
).
Tests whether the argument (arg0
) is a reference to the receiver object (this
).
The eq
method implements an equivalence relation on
non-null instances of AnyRef
, and has three additional properties:
x
and y
of type AnyRef
, multiple invocations of
x.eq(y)
consistently returns true
or consistently returns false
.x
of type AnyRef
, x.eq(null)
and null.eq(x)
returns false
.null.eq(null)
returns true
. When overriding the equals
or hashCode
methods, it is important to ensure that their behavior is
consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2
), they
should be equal to each other (o1 == o2
) and they should hash to the same value (o1.hashCode == o2.hashCode
).
true
if the argument is a reference to the receiver object; false
otherwise.
The equality method for reference types.
Returns true if this option is nonempty and the predicate
p
returns true when applied to this Option's value.
Returns this Option if it is nonempty and applying the predicate p
to
this Option's value returns true.
Returns this Option if it is nonempty and applying the predicate p
to
this Option's value returns false.
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize
method is invoked, as
well as the interaction between finalize
and non-local returns
and exceptions, are all platform dependent.
Finds the first element of the option satisfying a predicate, if any.
Finds the first element of the option satisfying a predicate, if any.
the predicate used to test elements.
an option value containing the first element in the option
that satisfies p
, or None
if none exists.
Returns the result of applying f
to this Option's value if
this Option is nonempty.
[use case] Builds a new collection by applying a function to all elements of this option and using the elements of the resulting collections.
Builds a new collection by applying a function to all elements of this option and using the elements of the resulting collections.
For example:
def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")
The type of the resulting collection is guided by the static type of option. This might cause unexpected results sometimes. For example:
// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet) // lettersOf will return a Set[Char], not a Seq def lettersOf(words: Seq[String]) = words.toSet flatMap (word => word.toSeq) // xs will be a an Iterable[Int] val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2) // ys will be a Map[Int, Int] val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)
the element type of the returned collection.
the function to apply to each element.
a new option resulting from applying the given collection-valued function
f
to each element of this option and concatenating the results.
[use case] Converts this option of traversable collections into a option formed by the elements of these traversable collections.
Converts this option of traversable collections into a option formed by the elements of these traversable collections.
The resulting collection's type will be guided by the static type of option. For example:
val xs = List(Set(1, 2, 3), Set(1, 2, 3)) // xs == List(1, 2, 3, 1, 2, 3) val ys = Set(List(1, 2, 3), List(3, 2, 1)) // ys == Set(1, 2, 3)
the type of the elements of each traversable collection.
a new option resulting from concatenating all element options.
Returns the result of applying f
to this Option's
value if the Option is nonempty.
Folds the elements of this option using the specified associative binary operator.
Folds the elements of this option using the specified associative binary operator.
a type parameter for the binary operator, a supertype of A
.
a neutral element for the fold operation; may be added to the result
an arbitrary number of times, and must not change the result (e.g., Nil
for list concatenation,
0 for addition, or 1 for multiplication.)
a binary operator that must be associative
the result of applying fold operator op
between all the elements and z
Applies a binary operator to a start value and all elements of this option, going left to right.
Applies a binary operator to a start value and all elements of this option, going left to right.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this option,
going left to right with the start value z
on the left:
op(...op(z, x_1), x_2, ..., x_n)
where x1, ..., xn
are the elements of this option.
Applies a binary operator to all elements of this option and a start value, going right to left.
Applies a binary operator to all elements of this option and a start value, going right to left.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this option,
going right to left with the start value z
on the right:
op(x_1, op(x_2, ... op(x_n, z)...))
where x1, ..., xn
are the elements of this option.
Returns true if this option is empty or the predicate
p
returns true when applied to this Option's value.
Apply the given procedure f
to the option's value,
if it is nonempty.
Apply the given procedure f
to the option's value,
if it is nonempty. Otherwise, do nothing.
the procedure to apply.
flatMap
map
[use case] Applies a function f
to all elements of this option.
Applies a function f
to all elements of this option.
Note: this method underlies the implementation of most other bulk operations. Subclasses should re-implement this method if a more efficient implementation exists.
the function that is applied for its side-effect to every element.
The result of function f
is discarded.
Returns string formatted according to given format
string.
Returns string formatted according to given format
string.
Format strings are as for String.format
(@see java.lang.String.format).
The generic builder that builds instances of Option
at arbitrary element types.
The generic builder that builds instances of Option
at arbitrary element types.
A representation that corresponds to the dynamic class of the receiver object.
A representation that corresponds to the dynamic class of the receiver object.
The nature of the representation is platform dependent.
a representation that corresponds to the dynamic class of the receiver object.
not specified by SLS as a member of AnyRef
Returns the option's value if the option is nonempty, otherwise
return the result of evaluating default
.
Returns the option's value if the option is nonempty, otherwise
return the result of evaluating default
.
the default expression.
Partitions this option into a map of options according to some discriminator function.
Partitions this option into a map of options according to some discriminator function.
Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new option.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to options such that the following invariant holds:
(xs partition f)(k) = xs filter (x => f(x) == k)
That is, every key k
is bound to a option of those elements x
for which f(x)
equals k
.
Partitions elements in fixed size options.
Partitions elements in fixed size options.
the number of elements per group
An iterator producing options of size size
, except the
last will be truncated if the elements don't divide evenly.
Iterator, method grouped
Tests whether this option is known to have a finite size.
Tests whether this option is known to have a finite size.
All strict collections are known to have finite size. For a non-strict
collection such as Stream
, the predicate returns true
if all
elements have been computed. It returns false
if the stream is
not yet evaluated to the end.
Note: many collection methods will not work on collections of infinite sizes.
true
if this collection is known to have finite size,
false
otherwise.
The hashCode method for reference types.
Selects the first element of this option.
Selects the first element of this option.
the first element of this option.
if the option is empty.
Optionally selects the first element.
Optionally selects the first element.
the first element of this option if it is nonempty,
None
if it is empty.
Selects all elements except the last.
Selects all elements except the last.
a option consisting of all elements of this option except the last one.
if the option is empty.
Iterates over the inits of this option.
Iterates over the inits of this option. The first value will be this
option and the final one will be an empty option, with the intervening
values the results of successive applications of init
.
an iterator over all the inits of this option
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
Returns true if the option is an instance of Some, false otherwise.
Test whether the dynamic type of the receiver object is T0
.
Test whether the dynamic type of the receiver object is T0
.
Note that the result of the test is modulo Scala's erasure semantics.
Therefore the expression 1.isInstanceOf[String]
will return false
, while the
expression List(1).isInstanceOf[List[String]]
will return true
.
In the latter example, because the type argument is erased as part of compilation it is
not possible to check whether the contents of the list are of the specified type.
true
if the receiver object is an instance of erasure of type T0
; false
otherwise.
Tests whether this option can be repeatedly traversed.
Tests whether this option can be repeatedly traversed.
true
Returns a singleton iterator returning the Option's value if it is nonempty, or an empty iterator if the option is empty.
Selects the last element.
Selects the last element.
The last element of this option.
If the option is empty.
Optionally selects the last element.
Optionally selects the last element.
the last element of this option$ if it is nonempty,
None
if it is empty.
Returns a Some containing the result of applying f
to this Option's
value if this Option is nonempty.
[use case] Builds a new collection by applying a function to all elements of this option.
Builds a new collection by applying a function to all elements of this option.
the element type of the returned collection.
the function to apply to each element.
a new option resulting from applying the given function
f
to each element of this option and collecting the results.
[use case] Finds the largest element.
Finds the largest element.
the largest element of this option.
[use case] Finds the smallest element.
Finds the smallest element.
the smallest element of this option
Displays all elements of this option in a string.
Displays all elements of this option in a string.
a string representation of this option. In the resulting string
the string representations (w.r.t. the method toString
)
of all elements of this option follow each other without any
separator string.
Displays all elements of this option in a string using a separator string.
Displays all elements of this option in a string using a separator string.
the separator string.
a string representation of this option. In the resulting string
the string representations (w.r.t. the method toString
)
of all elements of this option are separated by the string sep
.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this option in a string using start, end, and separator strings.
Displays all elements of this option in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this option. The resulting string
begins with the string start
and ends with the string
end
. Inside, the string representations (w.r.t. the method
toString
) of all elements of this option are separated by
the string sep
.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Equivalent to !(this eq that)
.
Equivalent to !(this eq that)
.
true
if the argument is not a reference to the receiver object; false
otherwise.
Returns false if the option is None
, true otherwise.
Returns false if the option is None
, true otherwise.
Implemented here to avoid the implicit conversion to Iterable.
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Returns this Option if it is nonempty,
otherwise return the result of evaluating alternative
.
Returns the option's value if it is nonempty,
or null
if it is empty.
Returns the option's value if it is nonempty,
or null
if it is empty.
Although the use of null is discouraged, code written to use
Option must often interface with code that expects and returns nulls.
val initalText: Option[String] = getInitialText val textField = new JComponent(initalText.orNull,20)
Returns a parallel implementation of this collection.
Returns a parallel implementation of this collection.
For most collection types, this method creates a new parallel collection by copying
all the elements. For these collection, par
takes linear time. Mutable collections
in this category do not produce a mutable parallel collection that has the same
underlying dataset, so changes in one collection will not be reflected in the other one.
Specific collections (e.g. ParArray
or mutable.ParHashMap
) override this default
behaviour by creating a parallel collection which shares the same underlying dataset.
For these collections, par
takes constant or sublinear time.
All parallel collections return a reference to themselves.
a parallel implementation of this collection
Partitions this option in two options according to a predicate.
Partitions this option in two options according to a predicate.
the predicate on which to partition.
a pair of options: the first option consists of all elements that
satisfy the predicate p
and the second option consists of all elements
that don't. The relative order of the elements in the resulting options
is the same as in the original option.
[use case] Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
the product of all elements in this option of numbers of type Int
.
Instead of Int
, any other type T
with an implicit Numeric[T]
implementation
can be used as element type of the option and as result type of product
.
Examples of such types are: Long
, Float
, Double
, BigInt
.
An iterator over all the elements of this product.
An iterator over all the elements of this product.
in the default implementation, an Iterator[Any]
A string used in the toString
methods of derived classes.
A string used in the toString
methods of derived classes.
Implementations may override this method to prepend a string prefix
to the result of toString
methods.
in the default implementation, the empty string
Reduces the elements of this option using the specified associative binary operator.
Reduces the elements of this option using the specified associative binary operator.
A type parameter for the binary operator, a supertype of A
.
A binary operator that must be associative.
The result of applying reduce operator op
between all the elements if the option is nonempty.
if this option is empty.
Optionally applies a binary operator to all elements of this option, going left to right.
Optionally applies a binary operator to all elements of this option, going left to right.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceLeft(op)
is this option is nonempty,
None
otherwise.
Reduces the elements of this option, if any, using the specified associative binary operator.
Reduces the elements of this option, if any, using the specified associative binary operator.
A type parameter for the binary operator, a supertype of A
.
A binary operator that must be associative.
An option value containing result of applying reduce operator op
between all
the elements if the collection is nonempty, and None
otherwise.
Applies a binary operator to all elements of this option, going right to left.
Applies a binary operator to all elements of this option, going right to left.
the result type of the binary operator.
the binary operator.
the result of inserting op
between consecutive elements of this option,
going right to left:
op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
where x1, ..., xn
are the elements of this option.
if this option is empty.
Optionally applies a binary operator to all elements of this option, going right to left.
Optionally applies a binary operator to all elements of this option, going right to left.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceRight(op)
is this option is nonempty,
None
otherwise.
The collection of type option underlying this TraversableLike
object.
The collection of type option underlying this TraversableLike
object.
By default this is implemented as the TraversableLike
object itself,
but this can be overridden.
[use case] Checks if the other iterable collection contains the same elements in the same order as this option.
Checks if the other iterable collection contains the same elements in the same order as this option.
the collection to compare with.
true
, if both collections contain the same elements in the same order, false
otherwise.
Computes a prefix scan of the elements of the collection.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z
may be applied more than once.
element type of the resulting collection
type of the resulting collection
neutral element for the operator op
the associative operator for the scan
combiner factory which provides a combiner
a new option containing the prefix scan of the elements in this option
Produces a collection containing cumulative results of applying the operator going left to right.
Produces a collection containing cumulative results of applying the operator going left to right.
the type of the elements in the resulting collection
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
an implicit value of class CanBuildFrom
which determines the result class That
from the current
representation type Repr
and the new element type B
.
collection with intermediate results
Produces a collection containing cumulative results of applying the operator going right to left.
Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.
Example:
List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
the type of the elements in the resulting collection
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
an implicit value of class CanBuildFrom
which determines the result class That
from the current
representation type Repr
and the new element type B
.
collection with intermediate results
(Changed in version 2.9.0) The behavior of scanRight
has changed. The previous behavior can be reproduced with scanRight.reverse.
A version of this collection with all of the operations implemented sequentially (i.
A version of this collection with all of the operations implemented sequentially (i.e. in a single-threaded manner).
This method returns a reference to this collection. In parallel collections, it is redefined to return a sequential implementation of this collection. In both cases, it has O(1) complexity.
a sequential view of the collection.
The size of this option.
The size of this option.
the number of elements in this option.
Selects an interval of elements.
Selects an interval of elements. The returned collection is made up
of all elements x
which satisfy the invariant:
from <= indexOf(x) < until
a option containing the elements greater than or equal to
index from
extending up to (but not including) index until
of this option.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
the distance between the first elements of successive groups (defaults to 1)
An iterator producing options of size size
, except the
last and the only element will be truncated if there are
fewer elements than size.
Iterator, method sliding
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
An iterator producing options of size size
, except the
last and the only element will be truncated if there are
fewer elements than size.
Iterator, method sliding
Splits this option into a prefix/suffix pair according to a predicate.
Splits this option into a prefix/suffix pair according to a predicate.
Note: c span p
is equivalent to (but possibly more efficient than)
(c takeWhile p, c dropWhile p)
, provided the evaluation of the
predicate p
does not cause any side-effects.
a pair consisting of the longest prefix of this option whose
elements all satisfy p
, and the rest of this option.
Splits this option into two at a given position.
Splits this option into two at a given position.
Note: c splitAt n
is equivalent to (but possibly more efficient than)
(c take n, c drop n)
.
the position at which to split.
a pair of options consisting of the first n
elements of this option, and the other elements.
Defines the prefix of this object's toString
representation.
Defines the prefix of this object's toString
representation.
a string representation which starts the result of toString
applied to this option. By default the string prefix is the
simple name of the collection class option.
[use case] Sums up the elements of this collection.
Sums up the elements of this collection.
the sum of all elements in this option of numbers of type Int
.
Instead of Int
, any other type T
with an implicit Numeric[T]
implementation
can be used as element type of the option and as result type of sum
.
Examples of such types are: Long
, Float
, Double
, BigInt
.
Selects all elements except the first.
Selects all elements except the first.
a option consisting of all elements of this option except the first one.
if the option is empty.
Iterates over the tails of this option.
Iterates over the tails of this option. The first value will be this
option and the final one will be an empty option, with the intervening
values the results of successive applications of tail
.
an iterator over all the tails of this option
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Selects first n elements.
Selects first n elements.
Tt number of elements to take from this option.
a option consisting only of the first n
elements of this option,
or else the whole option, if it has less than n
elements.
Selects last n elements.
Selects last n elements.
the number of elements to take
a option consisting only of the last n
elements of this option, or else the
whole option, if it has less than n
elements.
Takes longest prefix of elements that satisfy a predicate.
Takes longest prefix of elements that satisfy a predicate.
the longest prefix of this option whose elements all satisfy
the predicate p
.
[use case] Converts this option to an array.
Converts this option to an array.
an array containing all elements of this option.
An ClassTag
must be available for the element type of this option.
Converts this option to a mutable buffer.
Converts this option to a mutable buffer.
a buffer containing all elements of this option.
Converts this option to an indexed sequence.
Converts this option to an indexed sequence.
an indexed sequence containing all elements of this option.
Converts this option to an iterable collection.
Converts this option to an iterable collection. Note that
the choice of target Iterable
is lazy in this default implementation
as this TraversableOnce
may be lazy and unevaluated (i.e. it may
be an iterator which is only traversable once).
an Iterable
containing all elements of this option.
Returns an Iterator over the elements in this option.
Returns an Iterator over the elements in this option. Will return the same Iterator if this instance is already an Iterator.
an Iterator containing all elements of this option.
Returns a Right containing the given
argument right
if this is empty, or
a Left containing this Option's value
if this Option is nonempty.
Returns a singleton list containing the Option's value if it is nonempty, or the empty list if the Option is empty.
[use case] Converts this option to a map.
Converts this option to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U)
of this option.
Returns a Left containing the given
argument left
if this Option is empty, or
a Right containing this Option's value if
this is nonempty.
Converts this option to a sequence.
Converts this option to a sequence. As with toIterable
, it's lazy
in this default implementation, as this TraversableOnce
may be
lazy and unevaluated.
a sequence containing all elements of this option.
Converts this option to a set.
Converts this option to a set.
a set containing all elements of this option.
Converts this option to a stream.
Converts this option to a stream.
a stream containing all elements of this option.
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
a String representation of the object.
Converts this option to an unspecified Traversable.
Converts this option to an unspecified Traversable. Will return the same collection if this instance is already Traversable.
a Traversable containing all elements of this option.
Transposes this option of traversable collections into a option of options.
Transposes this option of traversable collections into a option of options.
the type of the elements of each traversable collection.
an implicit conversion which asserts that the
element type of this option is a Traversable
.
a two-dimensional option of options which has as nth row the nth column of this option.
(Changed in version 2.9.0) transpose
throws an IllegalArgumentException
if collections are not uniformly sized.
if all collections in this option are not of the same size.
Converts this option of pairs into two collections of the first and second half of each pair.
Converts this option of pairs into two collections of the first and second half of each pair.
the type of the first half of the element pairs
the type of the second half of the element pairs
an implicit conversion which asserts that the element type of this option is a pair.
a pair options, containing the first, respectively second half of each element pair of this option.
Converts this option of triples into three collections of the first, second, and third element of each triple.
Converts this option of triples into three collections of the first, second, and third element of each triple.
the type of the first member of the element triples
the type of the second member of the element triples
the type of the third member of the element triples
an implicit conversion which asserts that the element type of this option is a triple.
a triple options, containing the first, second, respectively third member of each element triple of this option.
Creates a non-strict view of a slice of this option.
Creates a non-strict view of a slice of this option.
Note: the difference between view
and slice
is that view
produces
a view of the current option, whereas slice
produces a new option.
Note: view(from, to)
is equivalent to view.slice(from, to)
the index of the first element of the view
the index of the element following the view
a non-strict view of a slice of this option, starting at index from
and extending up to (but not including) index until
.
Creates a non-strict view of this option.
Creates a non-strict view of this option.
a non-strict view of this option.
Necessary to keep Option from being implicitly converted to
Iterable in for
comprehensions.
[use case] Returns a option formed from this option and another iterable collection by combining corresponding elements in pairs.
Returns a option formed from this option and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
a new option containing pairs consisting of
corresponding elements of this option and that
. The length
of the returned collection is the minimum of the lengths of this option and that
.
[use case] Returns a option formed from this option and another iterable collection by combining corresponding elements in pairs.
Returns a option formed from this option and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
the element to be used to fill up the result if this option is shorter than that
.
the element to be used to fill up the result if that
is shorter than this option.
a new option containing pairs consisting of
corresponding elements of this option and that
. The length
of the returned collection is the maximum of the lengths of this option and that
.
If this option is shorter than that
, thisElem
values are used to pad the result.
If that
is shorter than this option, thatElem
values are used to pad the result.
[use case] Zips this option with its indices.
Zips this option with its indices.
A new option containing pairs consisting of all elements of this
option paired with their index. Indices start at 0
.
@example
List("a", "b", "c").zipWithIndex = List(("a", 0), ("b", 1), ("c", 2))
A syntactic sugar for out of order folding.
A syntactic sugar for out of order folding. See fold
.
Example:
scala> val a = LinkedList(1,2,3,4) a: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2, 3, 4) scala> val b = (a /:\ 5)(_+_) b: Int = 15
(Since version 2.10.0) use fold instead
(Since version 2.10.0) Use leftOfArrow instead
(Since version 2.10.0) Use resultOfEnsuring instead
Represents optional values. Instances of
Option
are either an instance of Some or the objectNone
.The most idiomatic way to use an Option instance is to treat it as a collection or monad and use
map
,flatMap
,filter
, orforeach
:Note that this is equivalent to
Because of how for comprehension works, if
None
is returned fromrequest.getParameter
, the entire expression results inNone
This allows for sophisticated chaining of Option values without having to check for the existence of a value.
A less-idiomatic way to use Option values is via pattern matching:
1.1, 16/01/2007
Many of the methods in here are duplicative with those in the Traversable hierarchy, but they are duplicated for a reason: the implicit conversion tends to leave one with an Iterable in situations where one could have retained an Option.