Suggestion: Allow merging of a wildcard import alias with a compile-time-only type alias of the same name

For projects with a lot of types with their own sets of functions, namespacing is of course a standard technique in programming to resolve naming conflicts between the functions of those types. The problem with namespacing in TypeScript (and JavaScript, by extension) is that it introduces an object-property hierarchy that can't be easily normalized to eliminate dead code and unused functions and classes.

ES2015 module syntax provided a nice solution for this - wildcard imports - but unfortunately that doesn't play nicely with TypeScript's merging of namespaces with types. I'd love to see a way to associate a module with an interface or type alias without introducing the compiled output overhead of TypeScript namespaces when those namespaces exist only to associate some functions with a related type name.

Proposal

If a compile-time-only type is imported with the same alias as the wildcard alias, either as default or otherwise, that type name would automatically merge with the wildcard alias, allowing the wildcard alias to also be used to reference the merged type alias:

// foo.ts
export interface Foo { /* ... */ }
export function create(): Foo { /* ... */ }
export default Foo;

// bar.ts
import Foo, * as Foo from './foo';
const foo: Foo = Foo.create();

// ------
// or:

// bar.ts
import * as Foo from './foo';
import { Foo } from './foo';
const foo: Foo = Foo.create();

Rationale

This is sort of already supported with TypeScript namespace merging, but TypeScript namespaces generate extra boilerplate that can't be easily tree-shaken at build time, and for which the indirection is baked into the final output, unlike wildcard imports, the indirection of which is discarded at build time by modern bundlers.

I can't do this:

import * as SortedSet from '@collectable/sorted-set';

// redundant/contrived, just for explanation purposes:
function add<T>(value: T, set: SortedSet<T>): SortedSet<T> {
  return SortedSet.add(value, set);
}

or this:

// ... the names can't be merged here:

import SortedSet, * as SortedSet from '@collectable/sorted-set';

// or here:

import * as SortedSet from '@collectable/sorted-set';
import SortedSet from '@collectable/sorted-set';

// or here:

import * as SortedSet from '@collectable/sorted-set';
import { SortedSet } from '@collectable/sorted-set';

Instead, I'd have to do this:

import * as SortedSet from '@collectable/sorted-set';

function add<T>(value: T, set: SortedSet.SortedSet<T>): SortedSet.SortedSet<T> {
  return SortedSet.add(value, set);
}

Or I could give SortedSet some kind of general type name, but this would then be too abstract if not performing a wildcard import:

import * as SortedSet from '@collectable/sorted-set';

function add<T>(value: T, set: SortedSet.Type<T>): SortedSet.Type<T> {
  return SortedSet.add(value, set);
}

// but now I'm forced to manually alias the type at the point of consumption:

import {Type as SortedSet, add} from '@collectable/sorted-set';

function add<T>(value: T, set: SortedSet<T>): SortedSet<T> {
  return add(value, set);
}

Alternatively I could export an alias of the SortedSet type as Type, but now I'm confusing the issue by having two different type names that mean the same thing.

I'm open to any solution which lets me associate a module with an interface or type alias; I just want the output to be optimal for ES2015, rather than optimal for TypeScript. For libraries that export a number of different type modules, where those modules implement common function names, this would be a very useful addition.

Inizia esaminando gli esempi della proposta relativi agli import wildcard e agli alias di tipo disponibili solo in fase di compilazione, poi segui il modo in cui TypeScript gestisce attualmente l’unione degli import namespace, type, default e denominati. Il lavoro è completo quando il comportamento del linguaggio è specificato e implementato senza l’overhead indesiderato a runtime dei namespace e i test coprono gli esempi e un output orientato a ES2015.