Remove `\xXX` char escapes from the language

[rust-highfive]

Issue by Valloric
Saturday Mar 08, 2014 at 21:19 GMT

For earlier discussion, see rust-lang/rust#12769

This issue was labelled with: B-RFC in the Rust repository

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\xXX is very misleading in Rust since it actually works exactly like \u00XX instead of the way it works in C, C++ and other languages. Example:

// this FAILS because left is [195, 191]
assert_eq!( bytes!( "\xFF"), bytes!( 255 ) ); 
// this SUCCEEDS
assert_eq!( bytes!( "\xFF"), bytes!( "\u00FF" ) );  

I understand the reasoning behind this (Rust strings are always UTF-8), but then \xXX shouldn't exist in the language. It brings nothing but confusion and it's functionality as implemented is the same as \u00XX.

[Ryman]

Using the modern syntax b"\xFF" this now has expected behavior. See: http://is.gd/3J0ysQ

[pnkfelix]

I think the original discussion thread is relevant here.

In particular, I think the real point is that this RFC is literally talking about char escapes. Yes, its example is then converting its input strings to byte arrays, and yes that is outdated syntax, but we still have support for \xXX in a string literal context, and it is probably still confusing. (Playpen illustration: http://is.gd/o7O43q )

So we should either remove support for \xXX from our string literals, or we should restrict it to only work for inputs in the ASCII range, as suggested a [1] few [2] times [3].

I'm going to write up an RFC for this right now, because it seems like a non-controversial change that would still have backwards-compatibility implications if we do not get it in for 1.0.

[Ryman]

@pnkfelix Ah yes, I'd overlooked the main argument. (Really shouldn't have commented at 4am :D)