44440e5c18
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]
43 lines
1.4 KiB
Rust
43 lines
1.4 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::mem::size_of;
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#[derive(PartialEq, Show)]
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enum Either<T, U> { Left(T), Right(U) }
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macro_rules! check {
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($t:ty, $sz:expr, $($e:expr, $s:expr),*) => {{
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assert_eq!(size_of::<$t>(), $sz);
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$({
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static S: $t = $e;
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let v: $t = $e;
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assert_eq!(S, v);
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assert_eq!(format!("{:?}", v).as_slice(), $s);
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assert_eq!(format!("{:?}", S).as_slice(), $s);
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});*
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}}
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}
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pub fn main() {
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check!(Option<u8>, 2,
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None, "None",
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Some(129u8), "Some(129u8)");
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check!(Option<i16>, 4,
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None, "None",
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Some(-20000i16), "Some(-20000i16)");
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check!(Either<u8, i8>, 2,
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Either::Left(132u8), "Left(132u8)",
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Either::Right(-32i8), "Right(-32i8)");
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check!(Either<u8, i16>, 4,
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Either::Left(132u8), "Left(132u8)",
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Either::Right(-20000i16), "Right(-20000i16)");
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}
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