76c313ceb1
If you were writing to something along the lines of `self.foo` then with the new closure rules it meant that you were borrowing `self` for the entirety of the closure, meaning that you couldn't format other fields of `self` at the same time as writing to a buffer contained in `self`. By lifting the borrow outside of the closure the borrow checker can better understand that you're only borrowing one of the fields at a time. This had to use type ascription as well in order to preserve trait object coercions.
29 lines
847 B
Rust
29 lines
847 B
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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#[allow(unused_must_use, dead_code)];
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use std::io::MemWriter;
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struct Foo<'a> {
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writer: &'a mut Writer,
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other: &'a str,
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}
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fn borrowing_writer_from_struct_and_formatting_struct_field(foo: Foo) {
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write!(foo.writer, "{}", foo.other);
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}
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pub fn main() {
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let mut w = MemWriter::new();
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write!(&mut w as &mut Writer, "");
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write!(&mut w, ""); // should coerce
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}
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