CODEWITHSUNDEEP
stringerror-handlingrustquotes
Zombo
Zombo

Reputation: 1

Return Result with unquoted string

If I have a file like this:

use std::error::Error;
fn main() -> Result<(), Box<dyn Error>> {   

   Err("May
June")?

}

I get this result:

Error: "May\nJune"

Is it possible to get the unquoted string on output? Like this:

Error: May
June

I tried this:

Err("May
June").map_err(|e|
   format!("{:?}", e)
)?

but it just made it worse:

Error: "\"May\\nJune\""

Upvotes: 0

Views: 177

Answers (2)

apetranzilla
apetranzilla

Reputation: 5949

It might be overkill to pull in an extra dependency for this, but you can use the terminator crate, which offers a new error type intended to be returned from main that delegates to the Display implementation when printed with Debug. Then your example would look like this...

use terminator::Terminator;

fn main() -> Result<(), Terminator> {   
   Err("May
June")?
}

...and the output would be this:

Error: May
June

Upvotes: 0

Kornel
Kornel

Reputation: 100120

You have to print the error yourself instead of relying on the default fallback implementation.

main() -> Result<…> prints Debug version of the error (where strings are escaped). It's intended as a quick'n'dirty solution for examples or playpens, and not for real programs where anyone would care about presentation of the output.

Use:

fn main() {
   if let Err(e) = run() {
       eprintln!("{}", e);
       std::process::exit(1);
   }
}

fn run() -> Result<(), Box<dyn Error>> {
   // etc
}

It will print the error using Display formatting.

There's nothing special about main()'s built-in error handling, so you're not losing anything by printing the error yourself.

There's also an alternative solution of implementing a custom Debug implementation on errors to make the Debug implementation print a non-debug one, but IMHO that's a hack, and needs more code than just doing the straightforward print. If you want that hack, have a look at the anyhow crate.

Upvotes: 5

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