function ripoff<T>(augmented: T & { a }): T {
  const { a, ...original } = augmented;
  return original;
}

import React, { Component } from 'react'

import { Counter } from './counter-render-prop'
import { Subtract } from '../types'

type ExtractFuncArguments<T> = T extends (...args: infer A) => any ? A : never;

// get props that Counter injects via children as a function
type InjectedProps = ExtractFuncArguments<Counter['props']['children']>[0];

// withCounter will enhance returned component by ExtendedProps
type ExtendedProps = { maxCount?: number };

// P is constrained to InjectedProps as we wanna make sure that wrapped component
// implements this props API
const withCounter = <P extends InjectedProps>(Cmp: React.ComponentType<P>) => {
  class WithCounter extends Component<
    // enhanced component will not include InjectedProps anymore as they are injected within render of this HoC and API surface is gonna be extended by ExtendedProps
    Subtract<P, InjectedProps> & ExtendedProps
  > {
    static displayName = `WithCounter(${Cmp.name})`;

    render() {
      const { maxCount, ...passThroughProps } = this.props;

      return (
       // we use Counter which has children as a function API for injecting props
        <Counter>
          {(injectedProps) =>
            maxCount && injectedProps.count >= maxCount ? (
              <p className="alert alert-danger">
                You've reached maximum count! GO HOME {maxCount}
              </p>
            ) : (
              // here cast to as P is needed otherwise compile error will occur
              <Cmp {...injectedProps as P} {...passThroughProps} />
            )
          }
        </Counter>
      );
    }
  }

  return WithCounter;
};

// CounterWannabe implement InjectedProps on it's props
class CounterWannabe extends Component<
  InjectedProps & { colorType?: 'primary' | 'secondary' | 'success' }
> {
  render() {
    const { count, inc, colorType } = this.props;

    const cssClass = `alert alert-${colorType}`;

    return (
      <div style={{ cursor: 'pointer' }} className={cssClass} onClick={inc}>
        {count}
      </div>
    );
  }
}

// if CounterWannabe would not implement InjectedProps this line would get compile error
const ExtendedComponent = withCounter(CounterWannabe);