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October 31, 2022 13:44
kotlin's style delegate in typescript
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function delegateTo(prop: string) { | |
const { __proto__ } = this | |
Object.setPrototypeOf(this, | |
new Proxy({}, { | |
get: (target, name) => { | |
target = this[prop] | |
if (name === prop) return target | |
if (name in __proto__) return __proto__[name] | |
return target ? target[name] : undefined | |
} | |
}) | |
) | |
} | |
export type Constructor<T=any> = new(...argv) => T | |
export function Decorator<T=any>(prop: string) { | |
return <any> function() { | |
delegateTo.call(this, prop) | |
} as Constructor<T> | |
} | |
function mixin<T>(...mixins: Array<Constructor>) { | |
const prototype = mixins.reduce( | |
(props, { prototype: __proto__ }) => { | |
let { prototype } = props | |
if (prototype) props = prototype | |
prototype = { __proto__ } | |
for (const key in props) prototype[key] = props[key] | |
return prototype | |
} | |
) | |
return <any> | |
Object.assign( | |
function(...argv) { | |
mixins.forEach(mixin => mixin.call(this, ...argv)) | |
}, | |
{ prototype } | |
) as Constructor<T> | |
} | |
export function delegate<To, From={}>(prop: string) { | |
return (Class: Constructor<From>) => | |
<any> class extends mixin(Class, Decorator(prop)) { | |
} as Constructor<To & From> | |
} | |
class A { | |
a() { console.log('a') } | |
} | |
@delegateTo<A>('aInst') | |
class B implements { aInst: A } { | |
constructor(private aInst: A) {} | |
} | |
new B(new A).a() |
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