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]
62 lines
1.8 KiB
Rust
62 lines
1.8 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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struct StateMachineIter<'a> {
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statefn: &'a StateMachineFunc<'a>
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}
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type StateMachineFunc<'a> = fn(&mut StateMachineIter<'a>) -> Option<&'static str>;
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impl<'a> Iterator for StateMachineIter<'a> {
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type Item = &'static str;
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fn next(&mut self) -> Option<&'static str> {
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return (*self.statefn)(self);
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}
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}
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fn state1(self_: &mut StateMachineIter) -> Option<&'static str> {
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self_.statefn = &(state2 as StateMachineFunc);
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//~^ ERROR borrowed value does not live long enough
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return Some("state1");
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}
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fn state2(self_: &mut StateMachineIter) -> Option<(&'static str)> {
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self_.statefn = &(state3 as StateMachineFunc);
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//~^ ERROR borrowed value does not live long enough
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return Some("state2");
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}
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fn state3(self_: &mut StateMachineIter) -> Option<(&'static str)> {
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self_.statefn = &(finished as StateMachineFunc);
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//~^ ERROR borrowed value does not live long enough
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return Some("state3");
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}
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fn finished(_: &mut StateMachineIter) -> Option<(&'static str)> {
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return None;
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}
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fn state_iter() -> StateMachineIter<'static> {
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StateMachineIter {
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statefn: &(state1 as StateMachineFunc) //~ ERROR borrowed value does not live long enough
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}
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}
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fn main() {
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let mut it = state_iter();
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println!("{:?}",it.next());
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println!("{:?}",it.next());
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println!("{:?}",it.next());
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println!("{:?}",it.next());
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println!("{:?}",it.next());
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}
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