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-rw-r--r--docs/dev/style.md33
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diff --git a/docs/dev/style.md b/docs/dev/style.md
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@@ -449,6 +449,39 @@ fn query_all(name: String, case_sensitive: bool) -> Vec<Item> { ... }
449fn query_first(name: String, case_sensitive: bool) -> Option<Item> { ... } 449fn query_first(name: String, case_sensitive: bool) -> Option<Item> { ... }
450``` 450```
451 451
452## Prefer Separate Functions Over Parameters
453
454If a function has a `bool` or an `Option` parameter, and it is always called with `true`, `false`, `Some` and `None` literals, split the function in two.
455
456```rust
457// GOOD
458fn caller_a() {
459 foo()
460}
461
462fn caller_b() {
463 foo_with_bar(Bar::new())
464}
465
466fn foo() { ... }
467fn foo_with_bar(bar: Bar) { ... }
468
469// BAD
470fn caller_a() {
471 foo(None)
472}
473
474fn caller_b() {
475 foo(Some(Bar::new()))
476}
477
478fn foo(bar: Option<Bar>) { ... }
479```
480
481**Rationale:** more often than not, such functions display "`false sharing`" -- they have additional `if` branching inside for two different cases.
482Splitting the two different control flows into two functions simplifies each path, and remove cross-dependencies between the two paths.
483If there's common code between `foo` and `foo_with_bar`, extract *that* into a common helper.
484
452## Avoid Monomorphization 485## Avoid Monomorphization
453 486
454Avoid making a lot of code type parametric, *especially* on the boundaries between crates. 487Avoid making a lot of code type parametric, *especially* on the boundaries between crates.