ConstraintHandling
Related Doc:
package core
Add constraint param <: bound if fromBelow is false, param >: bound otherwise.
Add constraint param <: bound if fromBelow is false, param >: bound otherwise.
bound is assumed to be in normalized form, as specified in firstTry and
secondTry of TypeComparer. In particular, it should not be an alias type,
lazy ref, typevar, wildcard type, error type. In addition, upper bounds may
not be AndTypes and lower bounds may not be OrTypes. This is assured by the
way isSubType is organized.
Add polytype pt, possibly with type variables tvars, to current constraint
and propagate all bounds.
Add polytype pt, possibly with type variables tvars, to current constraint
and propagate all bounds.
See Constraint#add
Solve constraint set for given type parameter param.
Solve constraint set for given type parameter param.
If fromBelow is true the parameter is approximated by its lower bound,
otherwise it is approximated by its upper bound. However, any occurrences
of the parameter in a refinement somewhere in the bound are removed. Also
wildcard types in bounds are approximated by their upper or lower bounds.
(Such occurrences can arise for F-bounded types).
The constraint is left unchanged.
the instantiating type
The current bounds of type parameter param
Can param be constrained with new bounds?
Check that constraint is fully propagated.
Check that constraint is fully propagated. See comment in Config.checkConstraintsPropagated
We are currently comparing polytypes.
We are currently comparing polytypes. Used as a flag for
optimization: when false, no need to do an expensive pruneLambdaParams
Perform op in a mode where all attempts to set frozen to true are ignored
If the constraint is frozen we cannot add new bounds to the constraint.
If the constraint is frozen we cannot add new bounds to the constraint.
The instance type of param in the current constraint (which contains param).
The instance type of param in the current constraint (which contains param).
If fromBelow is true, the instance type is the lub of the parameter's
lower bounds; otherwise it is the glb of its upper bounds. However,
a lower bound instantiation can be a singleton type only if the upper bound
is also a singleton type.
Test whether the lower bounds of all parameters in this constraint are a solution to the constraint.
Test whether the lower bounds of all parameters in this constraint are a solution to the constraint.
Constraint c1 subsumes constraint c2, if under c2 as constraint we have
for all poly params p defined in c2 as p >: L2 <: U2:
Constraint c1 subsumes constraint c2, if under c2 as constraint we have
for all poly params p defined in c2 as p >: L2 <: U2:
c1 defines p with bounds p >: L1 <: U1, and L2 <: L1, and U1 <: U2
Both c1 and c2 are required to derive from constraint pre, possibly
narrowing it with further bounds.
Instantiate param to tp if the constraint stays satisfiable
Instantiate param to tp if the constraint stays satisfiable
Methods for adding constraints and solving them.
What goes into a Constraint as opposed to a ConstrainHandler?
Constraint code is purely functional: Operations get constraints and produce new ones. Constraint code does not have access to a type-comparer. Anything regarding lubs and glbs has to be done elsewhere.
By comparison: Constraint handlers are parts of type comparers and can use their functionality. Constraint handlers update the current constraint as a side effect.