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No contextual typing for interfaces that extends interface with index signature #3804

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No contextual typing for interfaces that extends interface with index signature#3804
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By DesignDeprecated - use "Working as Intended" or "Design Limitation" instead

Description

@tinganho
Tingan Ho (tinganho)
opened on Jul 10, 2015

I was hoping this could work:

class A {
    public a: string;
}

interface B {
    [index: string]: A;
}

interface C extends B {
    a;
    b;
    c;
}

let c: C;
c.a.a // c.a of type A

but members of interface C has type any instead I was hoping I could get type A?

Notice I don't want to define directly:

let c: B;

because I need to pass C as a type with defined props.

Activity

  1. Tingan Ho (tinganho)
    changed the title [-]No contextual typings for interfaces that extends interface with index signature[/-] [+]No contextual typing for interfaces that extends interface with index signature[/+] on Jul 10, 2015
  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    By DesignDeprecated - use "Working as Intended" or "Design Limitation" instead
    on Jul 10, 2015

  3. RyanCavanaugh commented on Jul 10, 2015

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Jul 10, 2015
    Member

    Contextual typing applies to expressions, not declarations, so that part isn't exactly relevant.

    It's legal to declare members of type any (which is what you've done) even when you have an index signature. I don't think we would take a breaking change here.

  4. Ryan Cavanaugh (RyanCavanaugh)
    closed this as completedon Jul 10, 2015

  5. tinganho commented on Jul 12, 2015

    @tinganho
    Tingan Ho (tinganho)
    on Jul 12, 2015
    ContributorAuthor

    This is my problem right now:

    interface StyleRules extends Radium.StyleRules {
    feed: Radium.CSSStyleDeclaration;
    feedTitle: Radium.CSSStyleDeclaration;
    feedLoadMoreButton: Radium.CSSStyleDeclaration;
.   ...
}

    Having to repeat a type that I think could be inferred from a base interface. If not inferred maybe be able to reference the base signature value type?

  6. RyanCavanaugh commented on Jul 13, 2015

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Jul 13, 2015
    Member

    #1373 ?

  7. tinganho commented on Jul 14, 2015

    @tinganho
    Tingan Ho (tinganho)
    on Jul 14, 2015
    ContributorAuthor

    Yes sort of related. Though this suggestion is an interface derived from an
    interface/class. His suggestion where a class derived from a
    interface/class.

    tis 14 juli 2015 kl 00:45 skrev Ryan Cavanaugh notifications@github.com:

    #1373 #1373 ?

    —
    Reply to this email directly or view it on GitHub
    #3804 (comment)
    .

  8. microsoft
    locked and limited conversation to collaborators on Jun 19, 2018
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