55 lines
1.3 KiB
JavaScript
55 lines
1.3 KiB
JavaScript
// Counterexample with contravariant this type
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class C {
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next: this; // error (see below for exploit): `this` should only appear in
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// covariant positions
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}
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class D extends C { }
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var d = new D();
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(d: C).next = new C;
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(d.next: D); // sneaky
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class A {
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foo<X: this>(that: X) { } // error: can't hide contravariance using a bound
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}
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class B extends A {
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foo<Y: this>(that: Y) { } // error (see above, catches hidden override)
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}
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// covariance checks on this type in invariant positions
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class Invariant {
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out_object(): { _: this } { return { _: this }; }
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in_object(_: { _: this }) { }
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inout_object: { _: this };
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out_array(): Array<this> { return [this]; }
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in_array(_: Array<this>) { }
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inout_array: Array<this>;
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}
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// covariance checks on this type as type args
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class Misc {
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// Set<X> has invariant X
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out_set(): Set<this> { return new Set().add(this); }
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in_set(_: Set<this>) { }
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inout_set: Set<this>;
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// Promise<X> has covariant X
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async out_promise(): Promise<this> { return this; }
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in_promise(_: Promise<this>) { }
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inout_promise: Promise<this>;
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// Generator<X,Y,Z> has covariant X, covariant Y, contravariant Z
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*out_generator(): Generator<this,this,this> {
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yield this;
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return this;
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}
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in_generator(_: Generator<this,this,this>) { }
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inout_generator: Generator<this,this,this>;
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}
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