I want get Types from Generic Argment in tagged template literal function.

but typescript cant read from argment 'template'. It just read type as TemplateStringsArray.

const tag = <T extends ReadonlyArray<string>>(template: T, ...args: string[]) => {
  return {template, args};
};

const a = tag`hello ${'world'}`;
/**

const a: {
    template: TemplateStringsArray;
    args: string[];
}
*/

Is there any way to understand template as ['hello ', '']?

CodePudding user response：

The main problem here is that TemplateStringsArray is not parameterized. See this issue.

But you can still infer all but first argument of template literal function:

const tag = <
    Elem extends string,
    Template extends ReadonlyArray<Elem>,
    Arg extends string,
    Args extends Arg[]
>(template: Template, ...args: [...Args]) => ({ template, args })

// const a: {
//     template: TemplateStringsArray;
//     args: ["world", "kiwi"];
// }
const a = tag`hello ${'world'} ${'kiwi'}`;

Playground

If you want to infer whole string, you either should use ${} for each word or use regular function with infered string argument. If you want to learn more about type inference on function arguments you can take a look at my article

P.S. If you are interested in this feature, please like :thumb-up: above issue