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Is there a tool for #TypeScript that checks static type assertions similar to the following one?
// %inferred-type: (string | number | boolean)[]
const arr = [1, 'a', true];
I have written such a tool but it’s not ready for public consumption ATM, so such a tool already existing would save me the work of publishing what I have.
My tool is loosely similar to unit test runners such as Mocha—it enables static unit tests, if you will.
@rauschma It sounds like the new satisfies operator does what you need (new in v4.9):
> const arr = [1, 'a', true];
undefined
> arr satisfies (string | number | boolean)[]
{{{no typescript error}}}
> const arr2 = [1, 'a', true, new Date()];
undefined
> arr2 satisfies (string | number | boolean)[];
<repl>.ts:8:16 - error TS1360: Type '(string | number | boolean | Date)[]' does not satisfy the expected type '(string | number | boolean)[]'.
@vincentrolfs Alas, it’s not strict enough:
const a = 123;
(a satisfies number | boolean | string); // no error
@vincentrolfs@hachyderm.io@rauschma How about something like this? See also https://stackoverflow.com/questions/53807517/how-to-test-if-two-types-are-exactly-the-same.
@vincentrolfs Yes, that looks similar to some of the other suggestions in the replies! I’ll have to think about it—different from what I’m currently doing, with different pros and cons.