Pipeline Operator but for Generic Types

[hazae41]

Search Terms

pipeline operator
generic types

Suggestion

A pipeline operator but for generic types

Use Cases

This would be less ugly and more readable

Examples

The following

Promise<Signed<Message<String>>>

would become

Promise of Signed of Message of String

On an interface

interface Duck {
    quack(): Promise of String;
}

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.

[jcalz]

Near-duplicate of #34165

[dragomirtitian]

Similarly to #34165 I find the readability claim debatable.

Also what happens with generics with multiple type parameters ? would you use G of T1 and T2 ? How would you disambiguate something like G1 of G2 and T1 and T2 ? Is that G1<G2<T1, T2>> or G1<G2<T1>, T2>? While the angle brackets are not the prettiest bit of syntax they do make it clear where one type ends and the other continues.

[hazae41]

Promise of String
Promise of (String and number)

[jcalz]

Parentheses are too close to angle brackets for my taste; no human being uses parentheses or angle brackets to communicate. Instead of punctuation we should use a keyword to signify where a generic parameter list ends. Since reusing existing keywords is preferable to coining new ones (and helps the environment), a good one to use for this would be finally, which does a good job of signaling the end of something. And instead of and, a new keyword, we could re-use with, which is just sitting around gathering dust anyway. So: that means we can turn the completely incomprehensible

Pick<Map<string, Promise<number>>, "get">

into the human-friendly

Pick of Map of string with Promise of number finally finally "get" finally

[RyanCavanaugh]

@jcalz 😬

We're extremely conservative around adding syntax to the type space; new syntax needs to have very concrete upsides