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Narrow string and number types in equality checks and switch cases

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This commit is contained in:
Anders Hejlsberg 2016-10-12 14:12:32 -07:00
parent 4ccb3bb75c
commit 7497d81eec
1 changed files with 9 additions and 1 deletions
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10
src/compiler/checker.ts
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@ -8791,6 +8791,10 @@ namespace ts {
assumeTrue ? TypeFacts.EQUndefined : TypeFacts.NEUndefined;
return getTypeWithFacts(type, facts);
}
if (type.flags & TypeFlags.String && isTypeOfKind(valueType, TypeFlags.StringLiteral) ||
type.flags & TypeFlags.Number && isTypeOfKind(valueType, TypeFlags.NumberLiteral)) {
return assumeTrue? valueType : type;
}
if (type.flags & TypeFlags.NotUnionOrUnit) {
return type;
}
@ -8843,7 +8847,11 @@ namespace ts {
const clauseTypes = switchTypes.slice(clauseStart, clauseEnd);
const hasDefaultClause = clauseStart === clauseEnd || contains(clauseTypes, neverType);
const discriminantType = getUnionType(clauseTypes);
const caseType = discriminantType.flags & TypeFlags.Never ? neverType : filterType(type, t => isTypeComparableTo(discriminantType, t));
const caseType =
discriminantType.flags & TypeFlags.Never ? neverType :
type.flags & TypeFlags.String && isTypeOfKind(discriminantType, TypeFlags.StringLiteral) ? discriminantType :
type.flags & TypeFlags.Number && isTypeOfKind(discriminantType, TypeFlags.NumberLiteral) ? discriminantType :
filterType(type, t => isTypeComparableTo(discriminantType, t));
if (!hasDefaultClause) {
return caseType;
}