refactoring for extracting return type of a function

Search terms

refactoring extract return type function method interface inferred

Suggestion

A new refactoring for function expressions that extracts the return type of the function as an interface or type.

Use Cases

Imagine a complex function that combines many types of data into a complex object. Compiler can infer the return type, but writing it out by hand takes time. Type needs a name when you want to use it elsewhere in the code (for example as a parameter type for another function).

Examples

Imagine A, B, C, D are non trivial types. (e.g. objects with many properties)

before:

function fooFunc(a: A, b: B, c: C, d: D) {
  return {
    ...a,
    ...b,
    foo: {...c, d}
  }
}

after:

type FooFuncReturn = A & B & { foo: C & D }
// or when possible an interface type with would be even better

function fooFunc(a: A, b: B, c: C, d: D): FooFuncReturn {
  return {
    ...a,
    ...b,
    foo: {...c, d}
  }
}

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

L’issue non indica file, test o punti di ingresso. Inizia individuando l’infrastruttura di refactoring esistente di TypeScript, quindi definisci come l’estrazione richiesta del tipo restituito debba gestire le forme di tipo e interfaccia dell’esempio; il lavoro è completo quando il refactoring funziona per il caso d’uso di espressione di funzione indicato e il relativo output è coperto dai test.