microsoft / microsoft/TypeScript
Generic Type constraint from base classes, interfaces (Pass through)
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Suggestion
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Description
The ability to allow extends type constraint to be an abstract specification of base class, interface.
This also prevent duplication, by having to define the type constraint twice, reduces the need for unnecessary intermediate interfaces.
type ID = string
interface IShape<TID extends ID, Neasted>{
__ID: TID;
__Neasted : Neasted
}
interface ITSShape<T, ID>
{
__tsType: T;
__ID: ID;
}
interface IShapeType extends IShape<'T', boolean | number | null>
{
}
Not possible
interface IShapeTSType<T extends ['__Neasted']> extends IShapeType
{
__tsType : T;
}
interface IShapeTSType<T extends ['__Neasted']> extends IShape<'T', boolean | number | string>
{
__tsType : T;
}
interface IShapeTSType<T extends this['__Neasted']> extends IShapeType
{
__tsType : T;
}
interface IShapeTSType<T extends TShape['__Neasted'], TShape extends IShapeType> extends TShape
{
__tsType : T;
}
- 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.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by analyzing the proposed IShape, IShapeType, and IShapeTSType examples to clarify the intended generic constraint and inheritance semantics. Define what syntax should be accepted and verify that it avoids duplicated constraints without changing JavaScript output; the issue names no implementation files or tests.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100