43 lines
1.6 KiB
TypeScript
43 lines
1.6 KiB
TypeScript
import {reflect, CallSite} from 'typescript-rtti'
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type UnionToIntersection<U> =
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(U extends any ? (k: U) => void : never) extends ((k: infer I) => void)
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? I
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: never;
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export default function overload<T extends readonly [...any[]]>(
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imps: T, callSite?: CallSite): UnionToIntersection<T[number]> {
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const impTypes = reflect(callSite).parameters[0].elements
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return <any>((...a: any[]) => {
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for (let i = 0; i < imps.length; ++i) {
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const paramTypes = impTypes[i].type.parameters
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let match = true
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const haveArgs = a.length
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let onArg = 0
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for (const param of paramTypes) {
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if (param.isRest) {
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// All the rest of the arguments must be of param's type
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match = a.slice(onArg).every(
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arg => param.type.matchesValue(arg))
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break
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}
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if (onArg === haveArgs) {
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// We've used all of the arguments, so better be optional
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match = param.isOptional
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break
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}
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// This argument must match this param's type and both are used
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match = param.type.matchesValue(a[onArg])
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onArg += 1
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if (!match) break
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}
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// Make sure we used all the arguments
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match &&= (onArg == haveArgs)
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if (match) return imps[i](...a)
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}
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throw new TypeError(
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`Actual arguments ${a} of type ${a.map(arg => typeof arg)} `
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+ 'did not match any implementation')
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})
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}
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