Allow omission of generic type if its equal to the default type

Search Terms

generic, default, extends, equals, =

Suggestion

Allow the syntax extends = T in generics definition in place of extends T = T.

Currently

class Foo <T extends any = any> {}

Suggestion*

class Foo <T extends= any> {}

Use Cases

The problem of having to write <T extends any = any> revealed itself when I had a bit more complex type looking like keyof NetworkTransportProtocol that looked then somehow like this:

class Foo<T extends keyof system.NetworkTransportProtocol = keyof system.NetworkTransportProtocol> {}

which just was a lot of duplicated text.

class Foo<T extends= keyof system.NetworkTransportProtocol> {}

by reducing the duplicate information the whole syntax becomes better to read.

While I did focus on the default-case for class-generics. I believe this could also help with other definitions:

function foo <T extends=any>(bar: T) {}

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.

El issue no menciona archivos de implementación ni tests; empieza por localizar la gramática y los tests de TypeScript para las restricciones genéricas y los tipos predeterminados. Compara la sintaxis extends= propuesta para los genéricos de clases y funciones, y determina después el comportamiento requerido del parser y de la comprobación de tipos. Se considerará terminado cuando exista un diseño aceptado y una cobertura de tests que pase para la sintaxis propuesta.