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Improved handing of union types in type guards

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This commit is contained in:
Anders Hejlsberg
2015-01-12 14:51:20 -08:00
parent bf46e50f89
commit 59e266de02
6 changed files with 73 additions and 7 deletions
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14
src/compiler/checker.ts
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@@ -4709,13 +4709,21 @@ module ts {
if (!isTypeSubtypeOf(rightType, globalFunctionType)) {
return type;
}
// Target type is type of prototype property
var prototypeProperty = getPropertyOfType(rightType, "prototype");
if (!prototypeProperty) {
return type;
}
var prototypeType = getTypeOfSymbol(prototypeProperty);
// Narrow to type of prototype property if it is a subtype of current type
return isTypeSubtypeOf(prototypeType, type) ? prototypeType : type;
var targetType = getTypeOfSymbol(prototypeProperty);
// Narrow to target type if it is a subtype of current type
if (isTypeSubtypeOf(targetType, type)) {
return targetType;
}
// If current type is a union type, remove all constituents that aren't subtypes of target type
if (type.flags && TypeFlags.Union) {
return getUnionType(filter((<UnionType>type).types, t => isTypeSubtypeOf(t, targetType)));
}
return type;
}
// Narrow the given type based on the given expression having the assumed boolean value