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This commit is contained in:
Anders Hejlsberg
2017-06-09 15:39:24 -07:00
parent 76093c24cd
commit d27f4d4f15
1 changed files with 5 additions and 5 deletions
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10
src/compiler/checker.ts
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@@ -9504,7 +9504,7 @@ namespace ts {
}
}
else if (sourceSignatures.length === 1 && targetSignatures.length === 1) {
// For pure functions (functions with a single signature) we only erase type parameters for
// For simple functions (functions with a single signature) we only erase type parameters for
// the comparable relation. Otherwise, if the source signature is generic, we instantiate it
// in the context of the target signature before checking the relationship. Ideally we'd do
// this regardless of the number of signatures, but the potential costs are prohibitive due
@@ -15037,10 +15037,10 @@ namespace ts {
// outer call expression. Effectively we just want a snapshot of whatever has been
// inferred for any outer call expression so far.
const instantiatedType = instantiateType(contextualType, cloneTypeMapper(getContextualMapper(node)));
// If the contextual type is a generic pure function type, we instantiate the type with
// its own type parameters and type arguments. This ensures that the type parameters are
// not erased to type any during type inference such that they can be inferred as actual
// types from the contextual type. For example:
// If the contextual type is a generic function type with a single call signature, we
// instantiate the type with its own type parameters and type arguments. This ensures that
// the type parameters are not erased to type any during type inference such that they can
// be inferred as actual types from the contextual type. For example:
// declare function arrayMap<T, U>(f: (x: T) => U): (a: T[]) => U[];
// const boxElements: <A>(a: A[]) => { value: A }[] = arrayMap(value => ({ value }));
// Above, the type of the 'value' parameter is inferred to be 'A'.