流的条件类型
it1352
帮助1人
问题说明
是否可以根据条件在流中键入变量？这样的事情：
Is it possible to type a variable in flow based on a condition? Something like this:
const type = 'xyz';
const a: (type === 'xyz') ? number : string;
正确答案
#1
简短的回答是否定的。变量必须绑定到单个类型，其中可以包含类似 number |的联合类型串。在条件块内部，Flow可以推断出更专业的类型。例如：
The short answer is no. A variable must be bound to a single type, which can include a union type like number | string. Inside a conditional block Flow can infer a more specialised type. For example:
const a: number | string = "foo";
if(typeof a === "string"){
a.split(); // OK!
} else {
a.split(); // Error! a is a number
}
但请注意这些条件分支是静态的，并且它是有保证的在编译时，每个类型内的类型。
But notice that these conditional branches are static, and it's guaranteed at compile time what the type will be inside each.
这篇好文章是转载于：学新通技术网
