Evaluate compile-time constants

[n0izn0iz]

TypeScript Version: 3.5.0-dev.20190511

Search Terms:

compile-time operations numerical constants

Code

main.ts

const TWO: 2 = 1 + 1;

Expected behavior:

Transpiles without error

Actual behavior:

$> tsc main.ts

main.ts:1:7 - error TS2322: Type 'number' is not assignable to type '2'.

Playground Link:

https://www.typescriptlang.org/play/#src=const%20TWO%3A%202%20%3D%201%20%2B%201%3B

Related Issues:

[n0izn0iz]

Fun times:

const TWO: 2 = (1 + 3) as 2;
console.log(TWO);

Transpiles and executes, printing

4

EDIT: Please ignore this one

[MartinJohns]

Transpiles and executes, printing....

Type-assertions are a way to tell the compiler: "Trust me on this, I know what I'm doing and what this type is". The compiler trusts you. In this case the compiler resolves the type number, and you tell the compiler to assume it is the literal type 2. You get the same result with const two: 2 = 4 as 2;.

[jcalz]

Duplicate of #15645

[RyanCavanaugh]

Without some motivating use cases this doesn't look compelling as an area of investment. The intersection of areas where you have a finite domain of numbers (literals) but want to do some computation to map to one of those members seems very small.

[n0izn0iz]

const MESSAGE_BYTES = 32;
const BYTE_BITS = 8;
type SHA3Size = 224 | 256 | 384 | 512;
const SHA3_SIZE : SHA3Size = MESSAGE_BYTES * BYTE_BITS;
const hasher = SHA3(SHA3_SIZE)

I would understand if this not compelling enough.
Code is better than comments IMO. Also I guess my hatred for magic numbers is higher than the average.

[MartinJohns]

@n0izn0iz That looks more like "Units of measure": #364

[RyanCavanaugh]

8 * 32 seems like a much worse way to write 256, but I guess it's a matter of taste

[n0izn0iz]

Even if MESSAGE_BYTES is a constant used in another part of the program?

[Morglod]

https://github.com/Morglod/tsts

Currently working on comptime transformer

const numbers = [ 1, 2, 3, 4, 5, 6, 7, 8 ];
const result = comptime(() => {
    return numbers.reduce((total, x) => sum(total, x), 0);
});

to

const result = (() => { return (36); })();

[typescript-bot]

This issue has been marked as "Too Complex" and has seen no recent activity. It has been automatically closed for house-keeping purposes.