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Cleanup alloc advice

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Aleksey Kladov 2020-10-15 12:21:38 +02:00
parent 3a38554f86
commit dedfaa3844
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docs/dev/style.md
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@ -248,6 +248,8 @@ fn frbonicate(f: impl AsRef<Path>) {
# Premature Pessimization # Premature Pessimization
## Avoid Allocations
Avoid writing code which is slower than it needs to be. Avoid writing code which is slower than it needs to be.
Don't allocate a `Vec` where an iterator would do, don't allocate strings needlessly. Don't allocate a `Vec` where an iterator would do, don't allocate strings needlessly.
@ -267,6 +269,8 @@ if words.len() != 2 {
} }
``` ```
## Push Allocations to the Call Site
If allocation is inevitable, let the caller allocate the resource: If allocation is inevitable, let the caller allocate the resource:
```rust ```rust
@ -282,6 +286,9 @@ fn frobnicate(s: &str) {
} }
``` ```
This is better because it reveals the costs.
It is also more efficient when the caller already owns the allocation.
## Collection types ## Collection types
Prefer `rustc_hash::FxHashMap` and `rustc_hash::FxHashSet` instead of the ones in `std::collections`. Prefer `rustc_hash::FxHashMap` and `rustc_hash::FxHashSet` instead of the ones in `std::collections`.