41 lines
1.4 KiB
TypeScript
41 lines
1.4 KiB
TypeScript
class Chain<T> {
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constructor(public value: T) { }
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then<S extends T>(cb: (x: T) => S): Chain<S> {
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var t: T;
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var s: S;
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// Ok to go down the chain, but error to climb up the chain
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(new Chain(t)).then(tt => s).then(ss => t);
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// But error to try to climb up the chain
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(new Chain(s)).then(ss => t);
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// Staying at T or S should be fine
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(new Chain(t)).then(tt => t).then(tt => t).then(tt => t);
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(new Chain(s)).then(ss => s).then(ss => s).then(ss => s);
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return null;
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}
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}
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// Similar to above, but T is now constrained. Verify that the constraint is maintained across invocations
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interface I {
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x: number;
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}
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class Chain2<T extends I> {
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constructor(public value: T) { }
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then<S extends T>(cb: (x: T) => S): Chain2<S> {
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var i: I;
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var t: T;
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var s: S;
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// Ok to go down the chain, check the constraint at the end.
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// Should get an error that we are assigning a string to a number
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(new Chain2(i)).then(ii => t).then(tt => s).value.x = "";
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// Staying at T or S should keep the constraint.
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// Get an error when we assign a string to a number in both cases
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(new Chain2(i)).then(ii => t).then(tt => t).then(tt => t).then(tt => t).value.x = "";
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(new Chain2(i)).then(ii => s).then(ss => s).then(ss => s).then(ss => s).value.x = "";
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return null;
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}
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} |