Description
TypeScript Version: Nightly
Search Terms: parameter, inference, generic, function expression, arrow function expression
Expected behavior:
In function b, parameter a should be inferred as a: () => 42.
Actual behavior:
When using function expression instead of arrow function expression, parameter a is inferred as a: unknown.
Related Issues: #32230
Code
export declare function foo<A>(
options: {
a: A
b: (a: A) => void;
}
): void;
foo(
{
a: () => { return 42 },
b(a) {}, // a: () => 42
}
);
foo(
{
a: function () { return 42 },
b(a) {}, // a: unknown
}
);
foo(
{
a() { return 42 },
b(a) {}, // a: unknown
}
);Output
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
foo({
a: () => { return 42; },
b(a) { },
});
foo({
a: function () { return 42; },
b(a) { },
});
foo({
a() { return 42; },
b(a) { },
});Compiler Options
{
"compilerOptions": {
"noImplicitAny": true,
"strictNullChecks": true,
"strictFunctionTypes": true,
"strictPropertyInitialization": true,
"strictBindCallApply": true,
"noImplicitThis": true,
"noImplicitReturns": true,
"useDefineForClassFields": false,
"alwaysStrict": true,
"allowUnreachableCode": false,
"allowUnusedLabels": false,
"downlevelIteration": false,
"noEmitHelpers": false,
"noLib": false,
"noStrictGenericChecks": false,
"noUnusedLocals": false,
"noUnusedParameters": false,
"esModuleInterop": true,
"preserveConstEnums": false,
"removeComments": false,
"skipLibCheck": false,
"checkJs": false,
"allowJs": false,
"declaration": true,
"experimentalDecorators": false,
"emitDecoratorMetadata": false,
"target": "ES2017",
"module": "ESNext"
}
}Playground Link: Provided