Spreading tuple into generic/type arguments

Search Terms

• spreading generic parameters
• generic parameter spread
• tuple generic spread
• spreading generic argument
• spreading typeArgument
• spreading type argument

Suggestion

Allow spreading of a tuple type into type arguments.

The idea is that a tuple of n elements gets spread into generic arguments with r arguments. If n is larger than r, only the first r items are used. If n is smaller than r it is possible to add elements after the spread argument. E.g.

function foo<A, B, C, D>() {
}

type ThreeType = [Foo, Bar, Baz];

foo<...ThreeType, Delta>();

Use Cases

I find myself repeating complex generic types. Ideally I could shorten lengthy repetition into a single type.

Examples

dialog.open takes three generic arguments, these have to be repeated each call. This makes the call less legible and reduces DRYness.

const dialogRef = this.dialog.open<
    PrinterSelectDialogComponent,
    PrinterSelectDialogData,
    OfferProductPrinter>(
        PrinterSelectDialogComponent,
        {
            data: {
                printer,
            },
        },
    );

After this proposal

export type PrinterSelectDialog = [
    PrinterSelectDialogComponent,
    PrinterSelectDialogData,
    OfferProductPrinter,
];


const dialogRef = this.dialog.open<...PrinterSelectDialog>(PrinterSelectDialogComponent, {
    data: {
        service,
    },
});

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.

Comienza revisando la propuesta y sus ejemplos sobre el comportamiento previsto de la expansión de argumentos genéricos. Se considera terminado cuando se admitan expansiones de tuplas en argumentos de tipo, incluido el truncamiento cuando la tupla es más larga y los elementos finales cuando es más corta, sin cambiar el JavaScript generado.