Rust Programming

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Which is faster? (self.rust)

submitted 5 months ago* (last edited 5 months ago) by commander to c/rust@lemmy.ml

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let mut variable: Type;
loop {
    variable = value;
}

loop {
    let variable: Type = value;
}

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[+] asudox@lemmy.asudox.dev -18 points 5 months ago (3 children)

The second one is more expensive as you constantly are creating a new variable. In the first one you just constantly change the value of a variable.

[–] 1rre@discuss.tchncs.de 12 points 5 months ago* (last edited 5 months ago)

This is Rust not Python

They're both optimised out by the compiler. If you disable compiler optimisations, they're identical in machine code anyway, unless you introduce a second loop, in which case the first will be more memory efficient as the memory used in the first loop can be reused in the second loop, whereas if you declare the variable outside the loop it can't (again, without compiler optimisations, which make the whole comparison pointless).

[–] haroldstork@lemm.ee 10 points 5 months ago

This is just flat out false.