Write a function to define types.

Search Terms

type defination, functional type defination, meta, meta programming, dynamic type declaration

Suggestion

Write a function to define types.

Use Cases

Build a more complex type.

Examples

type MyType<T extends string>{
  if(T extends 'a'){
    return 'a' //type 'a'
  }
  if(T extends 'b'){
    return 'b' //type 'b'
  }
  return string
}

Checklist

My suggestion meets these guidelines:

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

该 issue 没有指出任何文件、测试或入口点。首先阅读 issue 讨论，以明确所提议的类型级函数的语法和语义，然后确定相关的编译器区域，并定义能够确立预期行为的测试。