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core: split into fmt::Show and fmt::String

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fmt::Show is for debugging, and can and should be implemented for
all public types. This trait is used with `{:?}` syntax. There still
exists #[derive(Show)].

fmt::String is for types that faithfully be represented as a String.
Because of this, there is no way to derive fmt::String, all
implementations must be purposeful. It is used by the default format
syntax, `{}`.

This will break most instances of `{}`, since that now requires the type
to impl fmt::String. In most cases, replacing `{}` with `{:?}` is the
correct fix. Types that were being printed specifically for users should
receive a fmt::String implementation to fix this.

Part of #20013

[breaking-change]
This commit is contained in:
Sean McArthur 2014-12-20 00:09:35 -08:00
parent 8efd9901b6
commit 44440e5c18
252 changed files with 1996 additions and 1366 deletions
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6
src/libfmt_macros/lib.rs
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@ -212,12 +212,12 @@ impl<'a> Parser<'a> {
self.cur.next();
}
Some((_, other)) => {
self.err(format!("expected `{}`, found `{}`", c, other)[]);
self.err(format!("expected `{:?}`, found `{:?}`", c, other)[]);
}
None => {
self.err(format!("expected `{}` but string was terminated",
self.err(format!("expected `{:?}` but string was terminated",
c)[]);
}
}
}
}