42 lines
1.2 KiB
JavaScript
42 lines
1.2 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.assertNever = assertNever;
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/**
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* Helper function for exhaustive checks of discriminated unions.
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* https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html
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*
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* @example
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*
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* type A = {type: 'a'};
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* type B = {type: 'b'};
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* type Union = A | B;
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*
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* function doSomething(arg: Union) {
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* if (arg.type === 'a') {
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* return something;
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* }
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*
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* if (arg.type === 'b') {
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* return somethingElse;
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* }
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*
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* // TS will error if there are other types in the union
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* // Will throw an Error when called at runtime.
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* // Use `assertNever(arg, true)` instead to fail silently.
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* return assertNever(arg);
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* }
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*/
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function assertNever(value, errorMessageOrNoThrow) {
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if (typeof errorMessageOrNoThrow === 'string') {
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throw new Error(errorMessageOrNoThrow);
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}
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if (typeof errorMessageOrNoThrow === 'function') {
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throw new Error(errorMessageOrNoThrow(value));
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}
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if (errorMessageOrNoThrow) {
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return value;
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}
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throw new Error("Unhandled discriminated union member: ".concat(JSON.stringify(value)));
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}
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exports.default = assertNever;
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