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clean up E0506 explanation

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This commit is contained in:
Guillaume Gomez 2020-04-06 14:20:01 +02:00
parent 1b521f5773
commit 3a10bdcfb6
1 changed files with 26 additions and 34 deletions
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60
src/librustc_error_codes/error_codes/E0506.md
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@ -1,4 +1,4 @@
This error occurs when an attempt is made to assign to a borrowed value. An attempt was made to assign to a borrowed value.
Erroneous code example: Erroneous code example:
@ -7,14 +7,12 @@ struct FancyNum {
num: u8, num: u8,
} }
fn main() { let mut fancy_num = FancyNum { num: 5 };
let mut fancy_num = FancyNum { num: 5 }; let fancy_ref = &fancy_num;
let fancy_ref = &fancy_num; fancy_num = FancyNum { num: 6 };
fancy_num = FancyNum { num: 6 }; // error: cannot assign to `fancy_num` because it is borrowed
// error: cannot assign to `fancy_num` because it is borrowed
println!("Num: {}, Ref: {}", fancy_num.num, fancy_ref.num); println!("Num: {}, Ref: {}", fancy_num.num, fancy_ref.num);
}
``` ```
Because `fancy_ref` still holds a reference to `fancy_num`, `fancy_num` can't Because `fancy_ref` still holds a reference to `fancy_num`, `fancy_num` can't
@ -27,13 +25,11 @@ struct FancyNum {
num: u8, num: u8,
} }
fn main() { let mut fancy_num = FancyNum { num: 5 };
let mut fancy_num = FancyNum { num: 5 }; let moved_num = fancy_num;
let moved_num = fancy_num; fancy_num = FancyNum { num: 6 };
fancy_num = FancyNum { num: 6 };
println!("Num: {}, Moved num: {}", fancy_num.num, moved_num.num); println!("Num: {}, Moved num: {}", fancy_num.num, moved_num.num);
}
``` ```
If the value has to be borrowed, try limiting the lifetime of the borrow using If the value has to be borrowed, try limiting the lifetime of the borrow using
@ -44,18 +40,16 @@ struct FancyNum {
num: u8, num: u8,
} }
fn main() { let mut fancy_num = FancyNum { num: 5 };
let mut fancy_num = FancyNum { num: 5 };
{ {
let fancy_ref = &fancy_num; let fancy_ref = &fancy_num;
println!("Ref: {}", fancy_ref.num); println!("Ref: {}", fancy_ref.num);
}
// Works because `fancy_ref` is no longer in scope
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
} }
// Works because `fancy_ref` is no longer in scope
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
``` ```
Or by moving the reference into a function: Or by moving the reference into a function:
@ -65,17 +59,15 @@ struct FancyNum {
num: u8, num: u8,
} }
fn main() {
let mut fancy_num = FancyNum { num: 5 };
print_fancy_ref(&fancy_num);
// Works because function borrow has ended
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
}
fn print_fancy_ref(fancy_ref: &FancyNum){ fn print_fancy_ref(fancy_ref: &FancyNum){
println!("Ref: {}", fancy_ref.num); println!("Ref: {}", fancy_ref.num);
} }
let mut fancy_num = FancyNum { num: 5 };
print_fancy_ref(&fancy_num);
// Works because function borrow has ended
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
``` ```