22 lines
1.2 KiB
TypeScript
22 lines
1.2 KiB
TypeScript
//// [inferentiallyTypingAnEmptyArray.ts]
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// April 2014, Section 4.6:
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// In the absence of a contextual type, the type of an array literal is C[], where C is the
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// Undefined type(section 3.2.6) if the array literal is empty, or the best common type of
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// the element expressions if the array literal is not empty.
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// When an array literal is contextually typed(section 4.19) by an object type containing a
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// numeric index signature of type T, each element expression is contextually typed by T and
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// the type of the array literal is the best common type of T and the types of the element
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// expressions.
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//
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// While the spec does not say it, an inferential type causes an empty array literal to have
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// the undefined[] type. In other words, the first clause from the excerpt above applies even
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// though there is a "contextual type" present. This is the intention, even though the spec
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// seems to imply the contrary.
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// Therefore, the following access to bar should not cause an error because we infer
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// the undefined[] type.
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declare function foo<T>(arr: T[]): T;
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foo([]).bar;
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//// [inferentiallyTypingAnEmptyArray.js]
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foo([]).bar;
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