flow-hoc-type.js

// @flow

import React from 'react'
import ReactDom from 'react-dom'

class InnerComponent extends React.Component<void, { myVal: number }, void>{
    props: { myVal: number }

    render = () =>
    <div>
      My value is {this.props.myVal}
    </div>
}


const HOC = <T>(Comp: Class<React.Component<any, { myVal: T}, any>>) =>
    ({xs}: {xs: Array<T>}) =>
    <div>
      {xs.forEach(x => <Comp myVal={x} />)}
    </div>

const ListComponent = HOC(InnerComponent)

const ListOfValues = [1,2,3]

ReactDom.render(<ListComponent xs={ListOfValues} />, document.getElementById('test'))

Error given by flow:

index.js:26
 26: ReactDom.render(<ListComponent xs={ListOfValues} />, document.getElementById('test'))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React element `ListComponent`
 17:     ({xs}: {xs: Array<T>}) =>
                           ^ T. This type is incompatible with
 17:     ({xs}: {xs: Array<T>}) =>
                           ^ some incompatible instantiation of `T`

index.js:26
 26: ReactDom.render(<ListComponent xs={ListOfValues} />, document.getElementById('test'))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React element `ListComponent`
 24: const ListOfValues = [1,2,3]
                           ^ number. This type is incompatible with
 17:     ({xs}: {xs: Array<T>}) =>
                           ^ some incompatible instantiation of `T`

index.js:26
 26: ReactDom.render(<ListComponent xs={ListOfValues} />, document.getElementById('test'))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React element `ListComponent`
 24: const ListOfValues = [1,2,3]
                             ^ number. This type is incompatible with
 17:     ({xs}: {xs: Array<T>}) =>
                           ^ some incompatible instantiation of `T`

index.js:26
 26: ReactDom.render(<ListComponent xs={ListOfValues} />, document.getElementById('test'))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React element `ListComponent`
 24: const ListOfValues = [1,2,3]
                               ^ number. This type is incompatible with
 17:     ({xs}: {xs: Array<T>}) =>
                           ^ some incompatible instantiation of `T`


Found 4 errors