| 1 | /*!
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| 2 | * Copyright (c) 2017-2018 by The Funfix Project Developers.
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| 3 | * Some rights reserved.
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| 4 | *
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| 5 | * Licensed under the Apache License, Version 2.0 (the "License");
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| 6 | * you may not use this file except in compliance with the License.
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| 7 | * You may obtain a copy of the License at
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| 8 | *
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| 9 | * http://www.apache.org/licenses/LICENSE-2.0
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| 10 | *
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| 11 | * Unless required by applicable law or agreed to in writing, software
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| 12 | * distributed under the License is distributed on an "AS IS" BASIS,
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| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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| 14 | * See the License for the specific language governing permissions and
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| 15 | * limitations under the License.
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| 16 | */
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| 17 |
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| 18 | /**
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| 19 | * Given a type `T` representing instances of a class `C`, the type
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| 20 | * `Constructor<T>` is the type of the class `C`.
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| 21 | *
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| 22 | * This type emulates
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| 23 | * [Class<T> from Flow]{@link https://flow.org/en/docs/types/utilities/#classt-a-classtoc-idtoc-class-hreftoc-classa}.
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| 24 | *
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| 25 | * Note that in TypeScript constructors can also be `protected` or `private`
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| 26 | * and unfortunately specifying `{ new(): T }` is thus insufficient.
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| 27 | * Which is why, for classes without a public constructor, we have to
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| 28 | * specify a `_funErasure` (static) member as a property, to help the compiler
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| 29 | * infer type `T`.
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| 30 | *
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| 31 | * Example:
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| 32 | *
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| 33 | * ```typescript
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| 34 | * class NumBox { constructor(public num: number) {} }
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| 35 | * class GenBox<A> { constructor(public a: A) {} }
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| 36 | *
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| 37 | * function getDefault<F>(ref: Constructor<F>): Option<F> {
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| 38 | * if ((ref as any)._default) return Some(ref._default)
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| 39 | * return None
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| 40 | * }
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| 41 | *
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| 42 | * (NumBox as any)._default = new NumBox(10)
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| 43 | * (GenBox as any)._default = new GenBox("value")
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| 44 | *
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| 45 | * const r1: Option<NumBox> = getDefault(NumBox)
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| 46 | * const r2: Option<GenBox<any>> = getDefault(GenBox)
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| 47 | * ```
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| 48 | *
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| 49 | * And for classes with a private constructor:
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| 50 | *
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| 51 | * ```typescript
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| 52 | * class PrivateBox<A> {
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| 53 | * private constructor(public a: A) {}
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| 54 | *
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| 55 | * static _funErasure: PrivateBox<any> // leaving undefined
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| 56 | * }
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| 57 | *
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| 58 | * const F = PrivateBox as any
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| 59 | * F._default = new F("hello")
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| 60 | *
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| 61 | * const r: Option<PrivateBox<any>> = getDefault(NumBox)
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| 62 | * ```
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| 63 | */
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| 64 | export type Constructor<T> =
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| 65 | { new(...args: any[]): T } | { readonly _Class: T }
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| 66 |
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| 67 | /**
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| 68 | * Lightweight encoding for higher kinded types.
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| 69 | *
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| 70 | * Inspired by the
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| 71 | * [Lightweight higher-kinded polymorphism]{@link https://www.cl.cam.ac.uk/~jdy22/papers/lightweight-higher-kinded-polymorphism.pdf}
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| 72 | * paper.
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| 73 | *
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| 74 | * Built to be compatible with other projects in the ecosystem.
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| 75 | */
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| 76 | export interface HK<URI, A> {
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| 77 | readonly _URI: URI
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| 78 | readonly _A: A
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| 79 | }
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| 80 |
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| 81 | /**
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| 82 | * Lightweight encoding for higher kinded types, the version for data
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| 83 | * types with two type parameters.
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| 84 | *
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| 85 | * See {@link HK} and {@link HK3}.
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| 86 | */
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| 87 | export interface HK2<URI, L, A> extends HK<URI, A> {
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| 88 | readonly _L: L
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| 89 | }
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| 90 |
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| 91 | /**
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| 92 | * Lightweight encoding for higher kinded types, the version for data
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| 93 | * types with two type parameters.
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| 94 | *
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| 95 | * See {@link HK} and {@link HK2}.
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| 96 | */
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| 97 | export interface HK3<URI, U, L, A> extends HK2<URI, L, A> {
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| 98 | readonly _U: U
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| 99 | }
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