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magurotuna/user_defined_type_guard.ts

Last active June 26, 2021 09:43
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user_defined_type_guard.ts
// https://github.com/denoland/deno_doc/pull/105
export function f1(val1: A | B): val1 is A {}
export function f2(val2: any): asserts val2 is string {}
export function f3(val3: any): asserts val3 {}
export function assertIsDefined<T>(val4: T): asserts val4 is NonNullable<T> {
if (val === undefined || val === null) {
throw new AssertionError(
`Expected 'val' to be defined, but received ${val}`
);
}
}
export class C {
isSomething(): this is Something {
return this instanceof Something;
}
}
export type A = string | number;
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