inferFromGenericFunctionReturnTypes2.ts(27,3): error TS2564: Property '_store' has no initializer and is not definitely assigned in the constructor.


==== inferFromGenericFunctionReturnTypes2.ts (1 errors) ====
    type Mapper<T, U> = (x: T) => U;
    
    declare function wrap<T, U>(cb: Mapper<T, U>): Mapper<T, U>;
    
    declare function arrayize<T, U>(cb: Mapper<T, U>): Mapper<T, U[]>;
    
    declare function combine<A, B, C>(f: (x: A) => B, g: (x: B) => C): (x: A) => C;
    
    declare function foo(f: Mapper<string, number>): void;
    
    let f1: Mapper<string, number> = s => s.length;
    let f2: Mapper<string, number> = wrap(s => s.length);
    let f3: Mapper<string, number[]> = arrayize(wrap(s => s.length));
    let f4: Mapper<string, boolean> = combine(wrap(s => s.length), wrap(n => n >= 10));
    
    foo(wrap(s => s.length));
    
    let a1 = ["a", "b"].map(s => s.length);
    let a2 = ["a", "b"].map(wrap(s => s.length));
    let a3 = ["a", "b"].map(wrap(arrayize(s => s.length)));
    let a4 = ["a", "b"].map(combine(wrap(s => s.length), wrap(n => n > 10)));
    let a5 = ["a", "b"].map(combine(identity, wrap(s => s.length)));
    let a6 = ["a", "b"].map(combine(wrap(s => s.length), identity));
    
    // This is a contrived class. We could do the same thing with Observables, etc.
    class SetOf<A> {
      _store: A[];
      ~~~~~~
!!! error TS2564: Property '_store' has no initializer and is not definitely assigned in the constructor.
    
      add(a: A) {
        this._store.push(a);
      }
    
      transform<B>(transformer: (a: SetOf<A>) => SetOf<B>): SetOf<B> {
        return transformer(this);
      }
    
      forEach(fn: (a: A, index: number) => void) {
          this._store.forEach((a, i) => fn(a, i));
      }
    }
    
    function compose<A, B, C, D, E>(
      fnA: (a: SetOf<A>) => SetOf<B>, 
      fnB: (b: SetOf<B>) => SetOf<C>, 
      fnC: (c: SetOf<C>) => SetOf<D>,
      fnD: (c: SetOf<D>) => SetOf<E>,
    ):(x: SetOf<A>) => SetOf<E>;
    /* ... etc ... */
    function compose<T>(...fns: ((x: T) => T)[]): (x: T) => T {
      return (x: T) => fns.reduce((prev, fn) => fn(prev), x);
    }
    
    function map<A, B>(fn: (a: A) => B): (s: SetOf<A>) => SetOf<B> {
      return (a: SetOf<A>) => {
        const b: SetOf<B> = new SetOf();
        a.forEach(x => b.add(fn(x)));
        return b;
      }
    }
    
    function filter<A>(predicate: (a: A) => boolean): (s: SetOf<A>) => SetOf<A> {
      return (a: SetOf<A>) => {
        const result = new SetOf<A>();
        a.forEach(x => {
          if (predicate(x)) result.add(x);
        });
       return result;
      }
    }
    
    const testSet = new SetOf<number>();
    testSet.add(1);
    testSet.add(2);
    testSet.add(3);
    
    const t1 = testSet.transform(
      compose(
        filter(x => x % 1 === 0),
        map(x => x + x),
        map(x => x + '!!!'),
        map(x => x.toUpperCase())
      )
    )
    
    declare function identity<T>(x: T): T;
    
    const t2 = testSet.transform(
      compose(
        filter(x => x % 1 === 0),
        identity,
        map(x => x + '!!!'),
        map(x => x.toUpperCase())
      )
    )
    