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Bug: Class extending & incompatible methods #14288

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Closed
Bug: Class extending & incompatible methods#14288
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Description

@alexcorvi
Ali A. Saleem (alexcorvi)
opened on Feb 24, 2017

TypeScript Version: 2.1.1

Code (playground link)

interface Details { 
    name: "Alex" | "Dan",
    age:number
}

class A {
    method(): Details { 
        return {
            name: "Alex", // this doesn't fire any error
            age:30
        }
    }
}

class B extends A {
    method() {
        return {
            name: "Alex", // this fires an error
            age:50
        }
    }
}

Expected behavior:

No compilation errors

Actual behavior:

An error that says:

Class 'B' incorrectly extends base class 'A'.
Types of property 'method' are incompatible.
Type '() => { name: string; age: number; }' is not assignable to type '() => Details'.
Type '{ name: string; age: number; }' is not assignable to type 'Details'.
Types of property 'name' are incompatible.
Type 'string' is not assignable to type '"Alex" | "Dan"'.

But method in class B is returning an object that is compatible with the declared interface an the error doesn't show up on class A method.

Activity

  1. alexcorvi commented on Feb 24, 2017

    @alexcorvi
    Ali A. Saleem (alexcorvi)
    on Feb 24, 2017
    Author

    Adding the Details interface as a declaration for the return type in the class B method does solve the issue.

    interface Details { 
    name: "Alex" | "Dan",
    age:number
}

class A {
    method(): Details { 
        return {
            name: "Alex",
            age:30
        }
    }
}

class B extends A {
    method(): Details {
        return {
            name: "Alex",
            age:50
        }
    }
}

    However, I don't have to add a declaration for the method() in class B since the class B is extending another class (B) where the method has a return declaration.

  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    Needs InvestigationThis issue needs a team member to investigate its status.
    on May 24, 2017

  3. mhegazy commented on Feb 8, 2018

    @mhegazy
    Mohamed Hegazy (mhegazy)
    on Feb 8, 2018
    Contributor

    Duplicate of #1373

    Related discussion in #6118 and #10570

  4. Mohamed Hegazy (mhegazy)
    added
    DuplicateAn existing issue was already created
    and removed
    Needs InvestigationThis issue needs a team member to investigate its status.
    on Feb 8, 2018

  5. typescript-bot commented on Feb 26, 2018

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Feb 26, 2018
    Contributor

    Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.

  6. TypeScript Bot (typescript-bot)
    closed this as completedon Feb 26, 2018
  7. microsoft
    locked and limited conversation to collaborators on Jul 3, 2018
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