Provides an alternative print and println macro that don't panic. #29464
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
The `println` and `print` macros provides a simple interface to output
content on the stdout of a program. The macros panic when writing to
stdout, and the failure condition could happen on external conditions.
Take the following rust code:
```rust
fn main() {
for _ in 0..10000 {
println!("line") {
}
}
```
Piping the program output to other utilities could cause the program to
panic, when the pipe is closed.
```bash
produce_logs | head
line
line
line
line
line
line
line
line
line
line
thread '<main>' panicked at 'failed printing to stdout: Broken pipe (os error 32)', ../src/libstd/io/stdio.rs:588
```
Instead of panicking, it would be interesting to allow the developer to
decide what to do with the error result, either ignoring it or panicking
on it's own. This commit implements `try_println` and `try_print` as an
alternative non-panicking macros.
The following code will not panic anymore when the pipe is closed.
```rust
fn main() {
for _ in 0..10000 {
if let Err(_) = try_println!("line") {
std::process::exit(0);
}
}
}
```
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Thanks for the PR! This unfortunately must be a change to the prelude of the standard library right now as we don't have macro imports or stability, and as a result this requires an RFC to land first (to have some design discussion about this and such). This has also come up before in issues like #14505, so there may be some good historical context there! For now, however, I'm going to close this, but if you need help writing an RFC please just let me know! |
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@alexcrichton Thanks for the feedback. |
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You might be interested in the discussion in #24821 if you haven't seen it yet. |
The
printlnandprintmacros provides a simple interface to outputcontent on the stdout of a program. The macros panic when writing to
stdout, and the failure condition could happen on external conditions.
Take the following rust code:
Piping the program output to other utilities could cause the program to
panic, when the pipe is closed.
Instead of panicking, it would be interesting to allow the developer to
decide what to do with the error result, either ignoring it or panicking
on it's own. This commit implements
try_printlnandtry_printas analternative non-panicking macros.
The following code will not panic anymore when the pipe is closed.