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add regression test for #16223 (NLL): use of collaterally moved value #49781
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// Copyright 2018 The Rust Project Developers. See the COPYRIGHT | ||
// file at the top-level directory of this distribution and at | ||
// http://rust-lang.org/COPYRIGHT. | ||
// | ||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
// option. This file may not be copied, modified, or distributed | ||
// except according to those terms. | ||
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// Regression test for #16223: without NLL the `if let` construct together with | ||
// the nested box-structure of `Root` causes an unwanted collateral move. | ||
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// The exact error prevented here is: | ||
// | ||
// error[E0382]: use of collaterally moved value: `(root.boxed.rhs as SomeVariant::B).0` | ||
// --> src/main.rs:55:29 | ||
// | | ||
// 56 | lhs: SomeVariant::A(a), | ||
// | - value moved here | ||
// 57 | rhs: SomeVariant::B(b), | ||
// | ^ value used here after move | ||
// | | ||
// = note: move occurs because the value has type `A`, which does not implement the `Copy` trait | ||
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// must-compile-successfully | ||
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#![feature(nll)] | ||
#![feature(box_patterns)] | ||
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struct Root { | ||
boxed: Box<SetOfVariants>, | ||
} | ||
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struct SetOfVariants { | ||
lhs: SomeVariant, | ||
rhs: SomeVariant, | ||
} | ||
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enum SomeVariant { | ||
A(A), | ||
B(B), | ||
} | ||
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struct A(String); | ||
struct B(String); | ||
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fn main() { | ||
let root = Root { | ||
boxed: Box::new(SetOfVariants { | ||
lhs: SomeVariant::A(A(String::from("This is A"))), | ||
rhs: SomeVariant::B(B(String::from("This is B"))), | ||
}), | ||
}; | ||
if let box SetOfVariants { | ||
lhs: SomeVariant::A(a), | ||
rhs: SomeVariant::B(b), | ||
} = root.boxed | ||
{ | ||
println!("a = {}", a.0); | ||
println!("b = {}", b.0); | ||
} | ||
} |
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You can use
*root.boxed
here if you want to avoid the box pattern.There was a problem hiding this comment.
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Thank you for the code review!
Your suggested code works and maybe this test should go with a dereference.
I haven't dereferenced
root.boxed
because it covers a nice use case where the entireroot.boxed
is only conditionally moved into the then-case of the if and otherwise can be further processed - this is not possible if you explicitely dereference it.I use this convenience a lot in my current project and at least to me it would be nice if this functionality was tested, too.