Enable to write async functions with the defined return type more simply, from :Promise<typename> to :typename@

[kamektx]

Search Terms

Promise, Abbreviation, At sign, At symbol

Suggestion

Now, in TypeScript, when you write the async function with the return type defined, you need to write like the following;

const myFunc = async (): Promise<boolean> => { 
    <...Tasks...>
    return true; 
}

However, it is redundant to write Promise<boolean> or Promise<number>.

The Array type has shortened forms such as boolean[] and number[], so it would be a good idea to write Promise<boolean> and Promise<number> as boolean@ and number@ by referring to them.

Use Cases

When you write async functions/methods.

Examples

Before

const myFunc1 = async (): Promise<boolean> => { return true; }
const myFunc2 = async (): Promise<number[]> => { return [1, 2, 3]; }

After

const myFunc1 = async (): boolean@ => { return true; }
const myFunc2 = async (): number[]@ => { return [1, 2, 3]; }

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.

[RyanCavanaugh]

This isn't really the kind of syntax we want to add to the type system.

[maroon1]

Async function always return a Promise, so why we have to explicitly return a Promise, rather than wrap the type of value by the type system.