CODEWITHSUNDEEP
rust
Mitch
Mitch

Reputation: 3416

Use const to calculate other const expressions with casting

Currently I have the following

const WIDTH : u16 = 1920;
const HEIGHT: u16 = 1080;
const PIXELS : usize = 1920 * 1080;

It would be nicer to have something like

const WIDTH : u16 = 1920;
const HEIGHT: u16 = 1080;
const PIXELS : usize = usize::from(WIDTH) * usize::from(HEIGHT);

But this will not compile. I assume this is because const are compile time variables and can't rely on the execution of usize::from. Is there an alternative?

Upvotes: 2

Views: 528

Answers (1)

Ibraheem Ahmed
Ibraheem Ahmed

Reputation: 13548

usize::from is not a constant function. If it were, your example would compile just fine. Instead, you can use simply cast the variables, which is all usize::from does internally:

const WIDTH : u16 = 1920;
const HEIGHT: u16 = 1080;
const PIXELS: usize = (WIDTH as usize) * (HEIGHT as usize);

Upvotes: 5

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