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[typescript conditional types playground] #typescript
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| // type tester for generics | |
| type ImmutablePrimitive = undefined | null | boolean | string | number | Function | |
| interface EmptyStruct { } | |
| // https://www.typescriptlang.org/docs/handbook/2/functions.html#other-types-to-know-about | |
| //type T = any | |
| //type T = unknown | |
| //type T = void | |
| //type T = undefined | |
| //type T = object | |
| //type T = never | |
| //type T = null | |
| //type T = boolean | |
| type T = string | |
| //type T = number | |
| //type T = Function | |
| //type T = () => number | |
| //type T = string[] | |
| //type T = Map<string, number> | |
| //type T = { foo: number[] } | |
| // // any unkn undefined object null string Function string[] Map<s,n> Struct | |
| type KeyofT = keyof T // || nv nv nv ... nv x x | |
| type ValuesOfT = T[keyof T] // any nv nv nv ... nv ... ... | |
| type T_is_any = 0 extends 1 & T ? true : false // any✔ | |
| type T_extends_any = T extends any ? true : false // any✔ undef✔ obj✔ nul✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| type any_extends_T_00 = any extends T ? true : false // any✔ ? ? ? ? ? ? ? ? | |
| type any_extends_T_01 = any extends [T] ? true : false // ?? ? ? ? ? | |
| type any_extends_T_10 = [any] extends T ? true : false // any✔ obj✔ str[]✔ | |
| type any_extends_T_11 = [any] extends [T] ? true : false // any✔ obj✔ fn✔ str[]✔ map✔ stct✔ | |
| type T_extends_unknown = T extends unknown ? true : false // any✔ undef✔ obj✔ nul✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| type unknown_extends_T = unknown extends T ? true : false // any✔ | |
| type T_extends_never_00 = T extends never ? true : false // ?? | |
| type T_extends_never_01 = T extends [never] ? true : false // ?? | |
| type T_extends_never_10 = [T] extends never ? true : false // | |
| type T_extends_never_11 = [T] extends [never] ? true : false // | |
| type never_extends_T = never extends T ? true : false // any✔ undef✔ obj✔ nul✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| type T_extends_string_0 = T extends string ? true : false // ?? | |
| type T_extends_ip_00 = T extends ImmutablePrimitive ? true : false // ?? undef✔ nul✔ str✔ fn✔ | |
| type T_extends_ip_01 = T extends [ImmutablePrimitive] ? true : false // ?? | |
| type T_extends_ip_10 = [T] extends ImmutablePrimitive ? true : false // | |
| type T_extends_ip_11 = [T] extends [ImmutablePrimitive] ? true : false // any✔ undef✔ nul✔ str✔ fn✔ | |
| type T_extends_obj_0 = T extends object ? true : false // obj✔ | |
| type T_extends_obj_01 = T extends [object] ? true : false // | |
| type T_extends_obj_10 = [T] extends object ? true : false // obj✔ str✔ | |
| type T_extends_obj_11 = [T] extends [object] ? true : false // obj✔ | |
| type T_extends_array_00 = T extends Array<infer E> ? true : false // ?? str[]✔ | |
| type T_extends_map_00 = T extends Map<infer K, infer V> ? true : false // ?? map✔ | |
| type T_extends_map_01 = T extends [Map<infer K, infer V>] ? true : false // ?? | |
| type T_extends_map_10 = [T] extends Map<infer K, infer V> ? true : false // | |
| type T_extends_map_11 = [T] extends [Map<infer K, infer V>] ? true : false // any✔ map✔ | |
| type T_extends_es_00 = T extends EmptyStruct ? true : false // ?? obj✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| type T_extends_es_01 = T extends [EmptyStruct] ? true : false // ?? | |
| type T_extends_es_10 = [T] extends EmptyStruct ? true : false // any✔ undef✔ obj✔ nul✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| type T_extends_es_11 = [T] extends [EmptyStruct] ? true : false // any✔ obj✔ str✔ fn✔ str[]✔ map✔ stct✔ | |
| export type ImmutableAny = Readonly<any> | |
| export type ImmutableArray<T> = ReadonlyArray<Immutable<T>> | |
| export type ImmutableMap<K, V> = ReadonlyMap<Immutable<K>, Immutable<V>> | |
| export type ImmutableSet<T> = ReadonlySet<Immutable<T>> | |
| export type ImmutableObject<T> = { +readonly [K in keyof T]: Immutable<T[K]> } | |
| export type Immutable<T> = true extends false ? never | |
| //: 0 extends 1 & T ? Readonly<any> | |
| : unknown extends T ? unknown | |
| : T extends Array<infer U> ? ImmutableArray<U> // | |
| : T extends Map<infer K, infer V> ? ImmutableMap<K, V> // any matches by being distributive!! | |
| : T extends Set<infer M> ? ImmutableSet<M> // any matches by being distributive!! | |
| : T extends EmptyStruct ? ImmutableObject<T> // any is distributive + this line is greedy with other container types, must be last! | |
| //: T extends undefined ? undefined | |
| //: T extends null ? null | |
| //: T extends boolean ? boolean | |
| //: T extends string ? string | |
| //: T extends number ? number | |
| //: T extends Function ? Function | |
| : T extends ImmutablePrimitive ? T // any matches by being distributive!! This makes the whole type "ANY" | |
| : never | |
| type I = Immutable<T> |
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