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@hraban hraban/runtime-mixin.ts
Last active Feb 6, 2018

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Typescript runtime mixins
// Inspired by:
// Once pipe operator is implemented in TS, use this example to check if it
// survives type checking.
// Describe mixed in functionality
interface Foo {
foo(): number;
interface Bar {
bar(): string;
// This is typechecked. Try changing e.g. the spelling of `foo`, or `3` into
// `"yes"`.
function mixinFoo<T>(x: T): T & Foo {
return Object.assign(x, {foo: function() { return 3; }});
// This is typechecked, too. Note the factory is not generic, but the returned
// function is.
function mixinBarFactory(msg: string) {
return function mixinBar<T>(x: T): T & Bar {
return Object.assign(x, {bar: function() { return msg; }});
// Random type to prove the point
class Something {}
function mixinTest(x: Something) {
const y = mixinBarFactory("hello")(mixinFoo(x));
y; // Check my type!
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