[rustc.git] / src / librustc_error_codes / error_codes / E0561.md

A non-ident or non-wildcard pattern has been used as a parameter of a function
pointer type.

Erroneous code example:

```compile_fail,E0561
type A1 = fn(mut param: u8); // error!
type A2 = fn(&param: u32); // error!
```

When using an alias over a function type, you cannot e.g. denote a parameter as
being mutable.

To fix the issue, remove patterns (`_` is allowed though). Example:

```
type A1 = fn(param: u8); // ok!
type A2 = fn(_: u32); // ok!
```

You can also omit the parameter name:

```
type A3 = fn(i16); // ok!
```
Commit	Line	Data
60c5eb7d XL	1	A non-ident or non-wildcard pattern has been used as a parameter of a function
	2	pointer type.
	3
	4	Erroneous code example:
	5
	6	```compile_fail,E0561
	7	type A1 = fn(mut param: u8); // error!
	8	type A2 = fn(&param: u32); // error!
	9	```
	10
	11	When using an alias over a function type, you cannot e.g. denote a parameter as
	12	being mutable.
	13
	14	To fix the issue, remove patterns (`_` is allowed though). Example:
	15
	16	```
	17	type A1 = fn(param: u8); // ok!
	18	type A2 = fn(_: u32); // ok!
	19	```
	20
	21	You can also omit the parameter name:
	22
	23	```
	24	type A3 = fn(i16); // ok!
	25	```