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]
30 lines
1.0 KiB
Rust
30 lines
1.0 KiB
Rust
// Copyright 2012-2014 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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extern crate collections;
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use std::collections::HashMap;
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fn check_strs(actual: &str, expected: &str) -> bool {
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if actual != expected {
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println!("Found {}, but expected {}", actual, expected);
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return false;
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}
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return true;
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}
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pub fn main() {
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let mut table = HashMap::new();
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table.insert("one".to_string(), 1i);
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table.insert("two".to_string(), 2i);
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assert!(check_strs(format!("{:?}", table).as_slice(), "HashMap {\"one\": 1i, \"two\": 2i}") ||
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check_strs(format!("{:?}", table).as_slice(), "HashMap {\"two\": 2i, \"one\": 1i}"));
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}
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