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]
41 lines
1.1 KiB
Rust
41 lines
1.1 KiB
Rust
// Copyright 2014 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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#[derive(Show)]
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struct Unit;
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#[derive(Show)]
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struct Tuple(int, uint);
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#[derive(Show)]
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struct Struct { x: int, y: uint }
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#[derive(Show)]
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enum Enum {
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Nullary,
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Variant(int, uint),
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StructVariant { x: int, y : uint }
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}
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macro_rules! t {
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($x:expr, $expected:expr) => {
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assert_eq!(format!("{:?}", $x), $expected.to_string())
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}
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}
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pub fn main() {
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t!(Unit, "Unit");
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t!(Tuple(1, 2), "Tuple(1i, 2u)");
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t!(Struct { x: 1, y: 2 }, "Struct { x: 1i, y: 2u }");
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t!(Enum::Nullary, "Nullary");
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t!(Enum::Variant(1, 2), "Variant(1i, 2u)");
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t!(Enum::StructVariant { x: 1, y: 2 }, "StructVariant { x: 1i, y: 2u }");
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}
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