关于 21章节第4小节 extends... ? : 的疑问，貌似有问题 #125

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coderwhytop opened this issue Oct 15, 2024 · 1 comment

coderwhytop commented Oct 15, 2024

你好，按照这里说的，type Z = ('x' | 1) extends (string | boolean) ? 'x' : 1; 分解为 ('x' extends string | boolean ? 'x' : 1) | (1 extends string | boolean ? 'x' : 1)，岂不是返回 'x' | 1 了？

ruanyf closed this as completed in

1725cbb

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ruanyf commented Oct 15, 2024

谢谢指出，已经更正。

正确说法是这个只对泛型有效。

type T1 = 'x' | 1;
type T2<T> = T extends (string | boolean) ? 'x' : 1;
type T3 = T2<T1>; // 'x' | 1

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