[rustc.git] / src / librustc_error_codes / error_codes / E0398.md

#### Note: this error code is no longer emitted by the compiler.

In Rust 1.3, the default object lifetime bounds are expected to change, as
described in [RFC 1156]. You are getting a warning because the compiler
thinks it is possible that this change will cause a compilation error in your
code. It is possible, though unlikely, that this is a false alarm.

The heart of the change is that where `&'a Box<SomeTrait>` used to default to
`&'a Box<SomeTrait+'a>`, it now defaults to `&'a Box<SomeTrait+'static>` (here,
`SomeTrait` is the name of some trait type). Note that the only types which are
affected are references to boxes, like `&Box<SomeTrait>` or
`&[Box<SomeTrait>]`. More common types like `&SomeTrait` or `Box<SomeTrait>`
are unaffected.

To silence this warning, edit your code to use an explicit bound. Most of the
time, this means that you will want to change the signature of a function that
you are calling. For example, if the error is reported on a call like `foo(x)`,
and `foo` is defined as follows:

```
# trait SomeTrait {}
fn foo(arg: &Box<SomeTrait>) { /* ... */ }
```

You might change it to:

```
# trait SomeTrait {}
fn foo<'a>(arg: &'a Box<SomeTrait+'a>) { /* ... */ }
```

This explicitly states that you expect the trait object `SomeTrait` to contain
references (with a maximum lifetime of `'a`).

[RFC 1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md
Commit	Line	Data
60c5eb7d XL	1	#### Note: this error code is no longer emitted by the compiler.
	2
	3	In Rust 1.3, the default object lifetime bounds are expected to change, as
	4	described in [RFC 1156]. You are getting a warning because the compiler
	5	thinks it is possible that this change will cause a compilation error in your
	6	code. It is possible, though unlikely, that this is a false alarm.
	7
	8	The heart of the change is that where `&'a Box<SomeTrait>` used to default to
	9	`&'a Box<SomeTrait+'a>`, it now defaults to `&'a Box<SomeTrait+'static>` (here,
	10	`SomeTrait` is the name of some trait type). Note that the only types which are
	11	affected are references to boxes, like `&Box<SomeTrait>` or
	12	`&[Box<SomeTrait>]`. More common types like `&SomeTrait` or `Box<SomeTrait>`
	13	are unaffected.
	14
	15	To silence this warning, edit your code to use an explicit bound. Most of the
	16	time, this means that you will want to change the signature of a function that
	17	you are calling. For example, if the error is reported on a call like `foo(x)`,
	18	and `foo` is defined as follows:
	19
	20	```
	21	# trait SomeTrait {}
	22	fn foo(arg: &Box<SomeTrait>) { /* ... */ }
	23	```
	24
	25	You might change it to:
	26
	27	```
	28	# trait SomeTrait {}
	29	fn foo<'a>(arg: &'a Box<SomeTrait+'a>) { /* ... */ }
	30	```
	31
	32	This explicitly states that you expect the trait object `SomeTrait` to contain
	33	references (with a maximum lifetime of `'a`).
	34
	35	[RFC 1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md