support template literal types

[DetachHead]

https://www.typescriptlang.org/docs/handbook/2/template-literal-types.html

[DetachHead]

i'm giving this a shot https://github.com/DetachHead/typescript-is

[DetachHead]

some things to consider:

• template literal types that only contain unions and/or booleans evaluate to unions of all possible string combinations. in cases like this, typescript-is already supports it because the type it evaluates to is just a regular union
• template literal types that contain ${string}, ${number}, etc. are implemented in such a way that leads to some unexpected behavior.
  • what should the compiled functions look like? i believe those problems could be easily solved if regex was used in place of the placeholders. for example, is<`foo${string}${number}bar`> would compile to something like

        function _3660(object) {
        ;
        if (object.match(/foo.*\dbar/))
            return {
                message: "validation failed at " + path.join(".") + ": expected template literal 'foo${string}${number}bar'",
                path: path.slice(),
                reason: {type: "string-literal", value: "foo${string}${number}bar"}
            };
        else
            return null;
    }

    though this would mean the type checker behaves differently to the typescript compiler, which i imagine is not desired. in that case the generated regex could look like /foo.\dbar/

  • is regex even an efficient solution? maybe it should just look ahead like the compiler does.

@woutervh- any advice?

[DetachHead]

i went with treating the values the same way the compiler does

[woutervh-]

Thanks again. Released v0.18.0 https://github.com/woutervh-/typescript-is/releases/tag/v0.18.0