46 lines
931 B
TypeScript
46 lines
931 B
TypeScript
// @declaration: true
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type Kind = "A" | "B"
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interface Entity {
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kind: Kind;
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}
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interface A extends Entity {
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kind: "A";
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a: number;
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}
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interface B extends Entity {
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kind: "B";
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b: string;
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}
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// Currently (2015-12-14), we write '"A" | "A"' and '"B" | "B"' to avoid
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// interpreting respective overloads as "specialized" signatures.
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// That way, we can avoid the need to look for a compatible overload
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// signature and simply check compatibility with the implementation.
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function hasKind(entity: Entity, kind: "A" | "A"): entity is A;
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function hasKind(entity: Entity, kind: "B" | "B"): entity is B;
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function hasKind(entity: Entity, kind: Kind): entity is Entity {
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return entity.kind === kind;
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}
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let x: A = {
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kind: "A",
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a: 100,
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}
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if (hasKind(x, "A")) {
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let a = x;
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}
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else {
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let b = x;
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}
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if (!hasKind(x, "B")) {
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let c = x;
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}
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else {
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let d = x;
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} |