TypeErasure

A type representing the semi-erasure of a derived value class, see SIP-15 where it's called "C$unboxed" for a class C. Derived value classes are erased to this type during Erasure (when semiEraseVCs = true) and subsequently erased to their underlying type during ElimErasedValueType. This type is outside the normal Scala class hierarchy: it is a subtype of no other type and is a supertype only of Nothing. This is because this type is only useful for type adaptation (see Erasure.Boxing#adaptToType).

The erased greatest lower bound of two erased type picks one of the two argument types.

This operation has the following the properties:

• Associativity and commutativity, because this method acts as the minimum of the total order induced by compareErasedGlb.
• Java compatibility: intersections that would be valid in Java code are erased like javac would erase them (a Java intersection is composed of exactly one class and one or more interfaces and always erases to the class).

Overload of erasedGlb to compare more than two types at once.

The erased least upper bound of two erased types is computed as follows

• if both argument are arrays of objects, an array of the erased lub of the element types
• if both arguments are arrays of same primitives, an array of this primitive
• if one argument is array of primitives and the other is array of objects, Object
• if one argument is an array, Object
• otherwise a common superclass or trait S of the argument classes, with the following two properties: S is minimal: no other common superclass or trait derives from S S is last : in the linearization of the first argument type tp1 there are no minimal common superclasses or traits that come after S. The reason to pick last is that we prefer classes over traits that way, which leads to more predictable bytecode and (?) faster dynamic dispatch.

The erasure of a top-level reference. Differs from normal erasure in that TermRefs are kept instead of being widened away.

The standard erasure of a Scala type. Value classes are erased as normal classes.

Like value class erasure, but value classes erase to their underlying type erasure

Does the (possibly generic) type tp have the same erasure in all its possible instantiations?

A predicate that tests whether a type is a legal erased type. Only asInstanceOf and isInstanceOf may have types that do not satisfy the predicate. ErasedValueType is considered an erased type because it is valid after Erasure (it is eliminated by ElimErasedValueType).

Is tp an abstract type or polymorphic type parameter, or another unbounded generic type?

Is Array[tp] a generic Array that needs to be erased to Object? This is true if among the subtypes of Array[tp] there is either:

• both a reference array type and a primitive array type (e.g. Array[_ <: Int | String], Array[_ <: Any])
• or two different primitive array types (e.g. Array[_ <: Int | Double]) In both cases the erased lub of those array types on the JVM is Object.

In addition, if isScala2 is true, we mimic the Scala 2 erasure rules and also return true for element types upper-bounded by a non-reference type such as in Array[_ <: Int] or Array[_ <: UniversalTrait].

The current context with a phase no later than erasure

The erasure that Scala 2 would use for this type.

The symbol's erased info. This is the type's erasure, except for the following symbols:

• For $asInstanceOf : [T]T
• For $isInstanceOf : [T]Boolean
• For all abstract types : = ?

sourceLanguage, isConstructor and semiEraseVCs are set based on the symbol.

The value class erasure of a Scala type, where value classes are semi-erased to ErasedValueType (they will be fully erased in ElimErasedValueType).