`x = void([Number, mod.BigNumber])` is already valid syntax in ECMAScript, and you can't change its semantics willy-nilly. How do you guarantee that those who have used `void` in their code in the past don't suddenly see unexpected type errors?
Also, can you make an example of how you could assign a default value to `x`
*and* support your type constraints? The problem that I see is that `void`
already evaluates its argument to `undefined`, which means that you would be
forced to do something like
```js
function CustomNumber(x = void([Number, mod.BigNumber]) || 42n) {
// …
}
```
which is arguably awkward.
On Sunday, June 3, 2018 9:53:34 AM CEST 喻恒春 wrote:
> Hello all,
>
> Sorry, I submitted a issue on the tc39/proposals/issues/146. It seems to be
> a mistake.
> This proposal adds static type constraints features to ECMAScript, based on
> the existing syntax, just use the features of void.
> It is located in the variable initial value or declares the parameter
> default value or the first statement of the body of the function.
>
>
>
> Example: not all
>
>
>
>
> ```js
>
> function CustomName(x = void ['', Number, mod.BigNumber]) {
>
> // Declarative results type, and the default value is not available
>
> void String;
>
> // same as void [String]
>
> // This function must eventually return a string
>
> // ...
>
> }
>
>
>
>
> class CustomClass {
>
> // ...
>
> }
>
>
>
>
> class PureStructure {
>
> constructor() {
>
> void {
>
> name: void [!'',String], // must be a name
>
> age: void [!0, Number], // must be age
>
> email: void String
>
> };
>
> }
>
> }
>
>
>
>
> class ClassPrototype {
>
> constructor() {
>
> void {
>
> name: String,
>
> age: Number,
>
> email: String
>
> };
>
> }
>
> }
>
>
>
>
> class FunctionPrototype {
>
> constructor() {
>
> void [[
>
> String,
>
> Number,
>
> String
>
> ]];
>
> }
>
>
>
> }
>
> ```
>
>
>
>
> Very embarrassing, my English is not awesome, so.........
>
>
>
>
> See https://github.com/achun/proposal-static-type-constraints-features
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