[rustc.git] / src / tools / clippy / src / docs / unnecessary_lazy_evaluations.txt

### What it does
As the counterpart to `or_fun_call`, this lint looks for unnecessary
lazily evaluated closures on `Option` and `Result`.

This lint suggests changing the following functions, when eager evaluation results in
simpler code:
 - `unwrap_or_else` to `unwrap_or`
 - `and_then` to `and`
 - `or_else` to `or`
 - `get_or_insert_with` to `get_or_insert`
 - `ok_or_else` to `ok_or`

### Why is this bad?
Using eager evaluation is shorter and simpler in some cases.

### Known problems
It is possible, but not recommended for `Deref` and `Index` to have
side effects. Eagerly evaluating them can change the semantics of the program.

### Example
```
// example code where clippy issues a warning
let opt: Option<u32> = None;

opt.unwrap_or_else(|| 42);
```
Use instead:
```
let opt: Option<u32> = None;

opt.unwrap_or(42);
```
Commit	Line	Data
f2b60f7d FG	1	### What it does
	2	As the counterpart to `or_fun_call`, this lint looks for unnecessary
	3	lazily evaluated closures on `Option` and `Result`.
	4
	5	This lint suggests changing the following functions, when eager evaluation results in
	6	simpler code:
	7	- `unwrap_or_else` to `unwrap_or`
	8	- `and_then` to `and`
	9	- `or_else` to `or`
	10	- `get_or_insert_with` to `get_or_insert`
	11	- `ok_or_else` to `ok_or`
	12
	13	### Why is this bad?
	14	Using eager evaluation is shorter and simpler in some cases.
	15
	16	### Known problems
	17	It is possible, but not recommended for `Deref` and `Index` to have
	18	side effects. Eagerly evaluating them can change the semantics of the program.
	19
	20	### Example
	21	```
	22	// example code where clippy issues a warning
	23	let opt: Option<u32> = None;
	24
	25	opt.unwrap_or_else(\|\| 42);
	26	```
	27	Use instead:
	28	```
	29	let opt: Option<u32> = None;
	30
	31	opt.unwrap_or(42);
	32	```