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Cannot use this to index private or protected properties #17362
Description
TypeScript Version: 2.4.1
Code
This works fine:
class Foo {
_foo: number;
foo(): this["_foo"] {
return this._foo;
}
}This works fine:
class Foo {
protected _foo: number;
foo(): Foo["_foo"] {
return this._foo;
}
}I expect this to work, but it does not work:
class Foo {
protected _foo: number;
foo(): this["_foo"] {
return this._foo;
}
}It fails with this error:
(4,10): error TS2536: Type '"_foo"' cannot be used to index type 'this'.
Activity
weswigham commentedon Jul 24, 2017
I think this is expected given our rules on indexed access types - given that the indexed access operator is defined in terms of
keyof T(see here) andkeyof Tis:So this will require adding an exception whereby private names are actually accessible when indexing
this.Pauan commentedon Jul 25, 2017
Wesley Wigham (@weswigham) But
Foo["_foo"]is the same situation, and it works fine.So does indexing on classes have an exception for private/protected members, but that exception wasn't applied to
this?mhegazy commentedon Nov 9, 2017
As Wesley Wigham (@weswigham) noted, this is the intended behavior. it becomes very hard to reason about these types in higher order if you have to carry around a context to know if the name is visible or not.
typescript-bot commentedon Nov 27, 2017
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.