Provide a way to alias namespaces

[falsandtru]

TypeScript should have a way to embed (type) namespaces. In the following case, assigned (embeded) namespace NS.A should have a C type.

TypeScript Version: master

Code

namespace NS_A {
  export class C {
  }
}
namespace NS {
  export var A = NS_A;
  export type A = NS_A;
}
var C = NS.A.C;
type C = NS.A.C;

Expected behavior:

$ node built/local/tsc.js --lib es6 -m commonjs --noEmit index.ts

Actual behavior:

$ node built/local/tsc.js --lib es6 -m commonjs --noEmit index.ts
index.ts(7,19): error TS2304: Cannot find name 'NS_A'.
index.ts(10,13): error TS2305: Module 'NS' has no exported member 'A'.

[RyanCavanaugh]

I've been thinking about this as well. We have var / const to alias a value, and type to alias a type, but no equivalent for namespace. We could even consider

namespace ns = foo;

for establishing namespace aliases.

[falsandtru]

Thanks!! I agree its syntax.

related: #5220

[falsandtru]

When extending namespaces, namespace merging is not good for immutability.

namespace ns = foo;
// foo is overwritten
namespace ns {
  export var bar;
}

Source namespaces shouldn't be changed by another module. So I think, an extends keyword for namespaces is a good solution.

// foo is not overwritten
namespace ns extends foo {
  export var bar;
}

[saschanaz]

It seems this existing syntax just works?

namespace NS_A {
  export class C {
  }
}
namespace NS {
  export import A = NS_A;
}
var C = NS.A.C;
type C = NS.A.C;

[zpdDG4gta8XKpMCd]

why won't we unify objects and namespaces instead of making them even more separated without a good reason?

related #8358

[falsandtru]

@saschanaz Oh, I didn't know its syntax. My problems were solved. Thanks for the great answer!!

[zpdDG4gta8XKpMCd]

as was shown it works fine as long as you separate values/functions from types, unifying them is what we all can benefit from

[RyanCavanaugh]

Looking to understand what the use cases for this are. Some real world code examples would be useful.

[falsandtru]

My use case:

https://github.com/falsandtru/pjax-api/blob/v3.3.0/src/layer/domain/router/model/eav/entity.ts#L17

Near case:

https://github.com/falsandtru/localsocket/blob/v0.4.4/src/layer/domain/indexeddb/model/socket/data.ts#L18-L23

As a related case of #9102 :

class C {
}
namespace C {
    export type T = void;
}
class D extends C {}
import D = C; // error