What does 'let x = x' do in Rust?
I saw this code in the wild:
fields.sort_by_key(|&(_, ref field)| field.tags().into_iter().min().unwrap());
let fields = fields;
What does the let fields = fields; line do? Why is it there?
rust
edited 7 hours ago
Shepmaster
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
add a comment |
I saw this code in the wild:
fields.sort_by_key(|&(_, ref field)| field.tags().into_iter().min().unwrap());
let fields = fields;
What does the let fields = fields; line do? Why is it there?
rust
edited 7 hours ago
Shepmaster
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
This line feel so nice! "Let fields be fields!"
– val
1 hour ago
add a comment |
I saw this code in the wild:
fields.sort_by_key(|&(_, ref field)| field.tags().into_iter().min().unwrap());
let fields = fields;
What does the let fields = fields; line do? Why is it there?
rust
edited 7 hours ago
Shepmaster
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
I saw this code in the wild:
fields.sort_by_key(|&(_, ref field)| field.tags().into_iter().min().unwrap());
let fields = fields;
What does the let fields = fields; line do? Why is it there?
rust
rust
edited 7 hours ago
Shepmaster
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
edited 7 hours ago
Shepmaster
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
edited 7 hours ago
Shepmaster
153k14301441
edited 7 hours ago
Shepmaster
153k14301441
edited 7 hours ago
Shepmaster
153k14301441
153k14301441
asked 8 hours ago
timtheliontimthelion
718920
asked 8 hours ago
timtheliontimthelion
718920
asked 8 hours ago
timtheliontimthelion
718920
718920
This line feel so nice! "Let fields be fields!"
– val
1 hour ago
add a comment |
This line feel so nice! "Let fields be fields!"
– val
1 hour ago
This line feel so nice! "Let fields be fields!"
– val
1 hour ago
This line feel so nice! "Let fields be fields!"
– val
1 hour ago
add a comment |
2 Answers
2
active
oldest
votes
It makes fields immutable again.
fields was previously defined as mutable (let mut fields = …;), to be used with sort_by_key which sorts in-place and requires the target to be mutable. The author has chosen here to explicitly prevent further mutability.
"Downgrading" a mutable binding to immutable is quite common in Rust.
Another common way to do this is to use a block expression:
let fields = {
let mut fields = …;
fields.sort_by_key(…);
fields
};
answered 8 hours ago
mcartonmcarton
6,43112535
add a comment |
The statement let var = var; makes var immutable and bound to its current value. fields was declared as mut earlier.
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
It makes fields immutable again.
fields was previously defined as mutable (let mut fields = …;), to be used with sort_by_key which sorts in-place and requires the target to be mutable. The author has chosen here to explicitly prevent further mutability.
"Downgrading" a mutable binding to immutable is quite common in Rust.
Another common way to do this is to use a block expression:
let fields = {
let mut fields = …;
fields.sort_by_key(…);
fields
};
answered 8 hours ago
mcartonmcarton
6,43112535
add a comment |
It makes fields immutable again.
fields was previously defined as mutable (let mut fields = …;), to be used with sort_by_key which sorts in-place and requires the target to be mutable. The author has chosen here to explicitly prevent further mutability.
"Downgrading" a mutable binding to immutable is quite common in Rust.
Another common way to do this is to use a block expression:
let fields = {
let mut fields = …;
fields.sort_by_key(…);
fields
};
answered 8 hours ago
mcartonmcarton
6,43112535
add a comment |
It makes fields immutable again.
fields was previously defined as mutable (let mut fields = …;), to be used with sort_by_key which sorts in-place and requires the target to be mutable. The author has chosen here to explicitly prevent further mutability.
"Downgrading" a mutable binding to immutable is quite common in Rust.
Another common way to do this is to use a block expression:
let fields = {
let mut fields = …;
fields.sort_by_key(…);
fields
};
answered 8 hours ago
mcartonmcarton
6,43112535
It makes fields immutable again.
fields was previously defined as mutable (let mut fields = …;), to be used with sort_by_key which sorts in-place and requires the target to be mutable. The author has chosen here to explicitly prevent further mutability.
"Downgrading" a mutable binding to immutable is quite common in Rust.
Another common way to do this is to use a block expression:
let fields = {
let mut fields = …;
fields.sort_by_key(…);
fields
};
answered 8 hours ago
mcartonmcarton
6,43112535
edited 7 hours ago
answered 8 hours ago
mcartonmcarton
6,43112535
answered 8 hours ago
mcartonmcarton
6,43112535
answered 8 hours ago
mcartonmcarton
6,43112535
6,43112535
add a comment |
add a comment |
The statement let var = var; makes var immutable and bound to its current value. fields was declared as mut earlier.
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
add a comment |
The statement let var = var; makes var immutable and bound to its current value. fields was declared as mut earlier.
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
add a comment |
The statement let var = var; makes var immutable and bound to its current value. fields was declared as mut earlier.
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
The statement let var = var; makes var immutable and bound to its current value. fields was declared as mut earlier.
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
answered 8 hours ago
Govind ParmarGovind Parmar
9,54553258
9,54553258
add a comment |
add a comment |
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This line feel so nice! "Let fields be fields!"
– val
1 hour ago