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-rw-r--r--docs/dev/style.md60
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diff --git a/docs/dev/style.md b/docs/dev/style.md
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@@ -368,6 +368,66 @@ impl ThingDoer {
368 368
369**Rationale:** not bothering the caller with irrelevant details, not mixing user API with implementor API. 369**Rationale:** not bothering the caller with irrelevant details, not mixing user API with implementor API.
370 370
371## Functions with many parameters
372
373Avoid creating functions with many optional or boolean parameters.
374Introduce a `Config` struct instead.
375
376```rust
377// GOOD
378pub struct AnnotationConfig {
379 pub binary_target: bool,
380 pub annotate_runnables: bool,
381 pub annotate_impls: bool,
382}
383
384pub fn annotations(
385 db: &RootDatabase,
386 file_id: FileId,
387 config: AnnotationConfig
388) -> Vec<Annotation> {
389 ...
390}
391
392// BAD
393pub fn annotations(
394 db: &RootDatabase,
395 file_id: FileId,
396 binary_target: bool,
397 annotate_runnables: bool,
398 annotate_impls: bool,
399) -> Vec<Annotation> {
400 ...
401}
402```
403
404**Rationale:** reducing churn.
405If the function has many parameters, they most likely change frequently.
406By packing them into a struct we protect all intermediary functions from changes.
407
408Do not implement `Default` for the `Config` struct, the caller has more context to determine better defaults.
409Do not store `Config` as a part of the `state`, pass it explicitly.
410This gives more flexibility for the caller.
411
412If there is variation not only in the input parameters, but in the return type as well, consider introducing a `Command` type.
413
414```rust
415// MAYBE GOOD
416pub struct Query {
417 pub name: String,
418 pub case_sensitive: bool,
419}
420
421impl Query {
422 pub fn all(self) -> Vec<Item> { ... }
423 pub fn first(self) -> Option<Item> { ... }
424}
425
426// MAYBE BAD
427fn query_all(name: String, case_sensitive: bool) -> Vec<Item> { ... }
428fn query_first(name: String, case_sensitive: bool) -> Option<Item> { ... }
429```
430
371## Avoid Monomorphization 431## Avoid Monomorphization
372 432
373Avoid making a lot of code type parametric, *especially* on the boundaries between crates. 433Avoid making a lot of code type parametric, *especially* on the boundaries between crates.