javascript - 流: Coercing an object-with-nullable-property to object-with-non-nullable-property?

Question

有没有一种方法可以表达两种相关类型(一种具有可空属性，一种不具有)，以便您可以在运行时进行检查后将一种强制转换为另一种？

例如 -

type Stat = {
  count: ?number,
}
type StatWithCount = {
  count: number
}

let stats: Array<Stat> = [{count: null}, {count: 2}]
let validStats: Array<StatWithCount> = []

for (let i=0; i<stats.length; i++) {
  const stat = stats[i]
  if (stat.count !== null) {
    validStats.push(stat) // This type is incompatible with object type
  }
}

https://flowtype.org/try/#0C4TwDgpgBAysCGwoF4oG8BQUoGMD2ArgHbABcUA-EQQLYBGEATgDQYC+GoksCwA6gEtgACwDChEinRZcEslGr0m7DBgA2EJAGdeW8gEFGjeCAA8cRAD4pAbTT5i86mrVtm6ByXIAmNgF11TSgAN3g1AQATC2A9KENjM2jBEXFHa1QbAIwAMzxGKAAKDSQBZAAGAG4oAVMdRC0AOg0iAHMRKoEAak6ASmlsYqg6pFRhrRsBAOwBbMLhhs8kAEJkVGc1PsxsbFDwqN0GsAItYQLhnpkONiA

Answer 1

据我所知，Flow不支持这个。

使用类型转换需要您自担风险:

if (stat.count !== null) {
  validStats.push(((stat: Object): StatWithCount))
}