[typescript conditional types playground] #typescript

condtypes.ts

// 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>