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Optional class properties by ahejlsberg · Pull Request #8625 · microsoft/TypeScript · GitHub
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Optional class properties #8625

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Merged
merged 11 commits into from
May 18, 2016
Merged

Optional class properties #8625

merged 11 commits into from
May 18, 2016

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@ahejlsberg
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@ahejlsberg ahejlsberg commented May 16, 2016 •
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This PR makes it possible to declare optional properties and methods in classes, similar to what is already permitted in interfaces. For example:

class Bar {
    a: number;
    b?: number;
    f() {
        return 1;
    }
    g?(): number;  // Body of optional method can be omitted
    h?() {
        return 2;
    }
}

When compiled in --strictNullChecks mode, optional properties and methods automatically have undefined included in their type. Thus, the b property above is of type number | undefined and the g method above is of type (() => number) | undefined. Type guards can be used to strip away the undefined part of the type:

function test(x: Bar) {
    x.a;  // number
    x.b;  // number | undefined
    x.f;  // () => number
    x.g;  // (() => number) | undefined
    let f1 = x.f();            // number
    let g1 = x.g && x.g();     // number | undefined
    let g2 = x.g ? x.g() : 0;  // number
}

mhegazy
mhegazy reviewed May 16, 2016
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tests/baselines/reference/objectTypesWithOptionalProperties.errors.txt Outdated
}

class C {
x?: number; // error
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comments are out of date now.

@mhegazy
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mhegazy commented May 16, 2016

can you add a declaration emit test.

@mhegazy
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mhegazy commented May 16, 2016

can you also add a test with --strictNullchecks and an optional parameter property declaration, e.g. constructor(private a?: number) { }

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mhegazy commented May 16, 2016

also another one for extending classes, making optionals non-optional, and making non-optionals optional.

@ahejlsberg ahejlsberg added this to the TypeScript 2.0 milestone May 18, 2016
@ahejlsberg ahejlsberg merged commit 9a22d08 into master May 18, 2016
@ahejlsberg ahejlsberg deleted the optionalClassProperties branch May 18, 2016 19:55
@RyanCavanaugh RyanCavanaugh mentioned this pull request May 24, 2016
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@CreepGin CreepGin mentioned this pull request Jun 3, 2016
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@CreepGin
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CreepGin commented Jun 3, 2016 •
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@ahejlsberg Nice job! Just curious, can decorators fetch information that can determine whether the target is declared optional?

@mhegazy
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mhegazy commented Jun 3, 2016

can decorators fetch information that can determine whether the target is declared optional?

no, see #8126

@Roam-Cooper
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Optional class properties don't seem to work for abstract properties in typescript 2.0.3, subclasses of the abstract class are forced to implement the property.

@aluanhaddad
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@Roam-Cooper that's the point of the abstract modifier, to require that an implementation is provided by a subclass. If it's optional you don't have to override it meaning it should not be abstract.

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Ah, yes, wasn't thinking straight! My bad. 😃

@bradenhs
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bradenhs commented Feb 24, 2017 •
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Does this PR enable making class getters optional? I can't figure out how to mark getters as optional. I have no idea where the question mark would go.

@Venryx
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Venryx commented Mar 15, 2017

@bradenhs I have the same question. Would be nice for my situation, where I want to make a custom derived class (which has getters) compatible with the base class definition/type-shape.

@bradenhs
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@Venryx I made an issue for this (#14417) but it was shot down. I don't think the guy reviewing the issue fully understood what I was getting at. You could create another issue and give a better explanation of the problem though. If you do let me know!

@Venryx Venryx mentioned this pull request Mar 16, 2017
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@ahejlsberg @mhegazy @CreepGin @Roam-Cooper @aluanhaddad @bradenhs @Venryx @msftclas