How to escape curly braces in a format string in Rust

string-formatting rust
Christoph picture Christoph · Aug 29, 2014 · Viewed 14.4k times · Source

I want to write this

write!(f, "{ hash:{}, subject: {} }", self.hash, self.subject)

But since curly braces have special meaning for formatting it's clear that I can't place the outer curly braces like that without escaping. So I tried to escape them.

write!(f, "\{ hash:{}, subject: {} \}", self.hash, self.subject)

Rust doesn't like that either. Then I read this:

The literal characters {, }, or # may be included in a string by preceding them with the \ character. Since \ is already an escape character in Rust strings, a string literal using this escape will look like "\{".

So I tried

write!(f, "\\{ hash:{}, subject: {} \\}", self.hash, self.subject)

But that's also not working. :-(

Answer

nos picture nos · Aug 29, 2014

You might be reading some out of date docs (e.g. for Rust 0.9)

As of Rust 1.0, the way to escape { and } is with another { or }

write!(f, "{{ hash:{}, subject: {} }}", self.hash, self.subject)

The literal characters { and } may be included in a string by preceding them with the same character. For example, the { character is escaped with {{ and the } character is escaped with }}.

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