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Strict object literal check fails when infered to type containing string literal type #7085
Description
Hi,
This issue might be linked to #6167 ( particularly widening i guess) or #6554, but i did not find any details the bellow case:
interface Test {
value: string;
comparator:"equals"|"isGreater";
}
function applyTest(value: string, testval:Test) {
return "ok";
}
let tt = {value: "test", comparator:"equals"};
applyTest("ko",tt);when i compile using tsc (typescript@1.9.0-dev.20160215) i get a warning
test.ts(11,16): error TS2345: Argument of type '{ value: string; comparator: string; }' is not assignable to parameter of type 'Test'.
Types of property 'comparator' are incompatible.
Type 'string' is not assignable to type '"equals" | "isGreater"'.
Type 'string' is not assignable to type '"isGreater"'.
Activity
weswigham commentedon Feb 15, 2016
Apply a type annotation such as
let tt: Test = { ... }. TS only infers string literal types in type positions and when contextually appropriate based on type information. Since TS doesn't do use-site analysis,ttgets typed soled by its definition, which is{value: string, comparator: string}, as there's no casts/annotations indicating it should use a literal type.