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Lint for &String::into(): String on final use of input string #61994
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Yeah, I'm not sure I like that change. I always liked that potentially expensive operations like clone() were explicit and searchable. Also, I usually think of
.into()and::fromas a move, not a copy, since it consumes the callee.In C++, it's extremely easy to make copies accidentally and while
impl From<&String> for Stringmight be reasonably harmless, I feel like animpl <T: Clone> From<&T> for Tkinda pushes Rust too far in that direction.If that feature is here to stay, then I would probably always enable this lint as an error in my projects
PR #59825 added a
impl From<&String> for String.While perusing the
rustcsource, I am now seeing instances ofStringvalues being constructed and then passed via-reference into a function that wants aString. These would not have compiled without the change added by PR #59825.It might be worthwhile to try to make a lint that detects the last use of a
Stringthat is then being used as an argument to&which is then itself passed to this conversion method (which effectively hides the clone taking place.(You can see discussion of the hidden clone on #59827; I'm not seeking debate on the merits of PR #59825. I just am wondering if we could easily highlight the unnecessary clones via a lint.)