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Add truthy/falsey guards for nullable types

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This commit is contained in:
Anders Hejlsberg
2016-02-16 09:51:49 -08:00
parent 586c3ac86f
commit bf89530e36
1 changed files with 6 additions and 0 deletions
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6
src/compiler/checker.ts
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@@ -6993,6 +6993,10 @@ namespace ts {
return type;
function narrowTypeByTruthiness(type: Type, expr: Identifier, assumeTrue: boolean): Type {
return strictNullChecks && assumeTrue && getResolvedSymbol(expr) === symbol ? getNonNullableType(type) : type;
}
function narrowTypeByEquality(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
// Check that we have 'typeof <symbol>' on the left and string literal on the right
if (expr.left.kind !== SyntaxKind.TypeOfExpression || expr.right.kind !== SyntaxKind.StringLiteral) {
@@ -7195,6 +7199,8 @@ namespace ts {
// will be a subtype or the same type as the argument.
function narrowType(type: Type, expr: Expression, assumeTrue: boolean): Type {
switch (expr.kind) {
case SyntaxKind.Identifier:
return narrowTypeByTruthiness(type, <Identifier>expr, assumeTrue)
case SyntaxKind.CallExpression:
return narrowTypeByTypePredicate(type, <CallExpression>expr, assumeTrue);
case SyntaxKind.ParenthesizedExpression: