Mixing
Is there a way to split up a variable inside an Option without having to use if statements?
I want the code below to work, but since map() takes ownership of Option, and there doesn't seem to be a clone() function for Option, the following doesn't compile.
fn main() {
struct ItemA {
a: String,
b: String,
}
let foo = Some(ItemA {
a: "A String".to_owned(),
b: "B String".to_owned(),
});
// OR
// let foo = None;
let opA: Option<String> = foo.map(|c| c.a);
let opB: Option<String> = foo.map(|c| c.b);
}
error[E0382]: use of moved value: `foo`
--> src/main.rs:15:31
|
14 | let opA: Option<String> = foo.map(|c| c.a);
| --- value moved here
15 | let opB: Option<String> = foo.map(|c| c.b);
| ^^^ value used here after move
|
= note: move occurs because `foo` has type `std::option::Option<main::ItemA>`, which does not implement the `Copy` trait
It would be nice if opA can take ownership of ItemA.a (so it doesn't have to clone the strings), and opB can take ownership of ItemA.b
Is this possible to do without having to use if statements to check if the Option is Some or None, unwrapping, and wrapping it back up individually.
rust ownership
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
add a comment |
I want the code below to work, but since map() takes ownership of Option, and there doesn't seem to be a clone() function for Option, the following doesn't compile.
fn main() {
struct ItemA {
a: String,
b: String,
}
let foo = Some(ItemA {
a: "A String".to_owned(),
b: "B String".to_owned(),
});
// OR
// let foo = None;
let opA: Option<String> = foo.map(|c| c.a);
let opB: Option<String> = foo.map(|c| c.b);
}
error[E0382]: use of moved value: `foo`
--> src/main.rs:15:31
|
14 | let opA: Option<String> = foo.map(|c| c.a);
| --- value moved here
15 | let opB: Option<String> = foo.map(|c| c.b);
| ^^^ value used here after move
|
= note: move occurs because `foo` has type `std::option::Option<main::ItemA>`, which does not implement the `Copy` trait
It would be nice if opA can take ownership of ItemA.a (so it doesn't have to clone the strings), and opB can take ownership of ItemA.b
Is this possible to do without having to use if statements to check if the Option is Some or None, unwrapping, and wrapping it back up individually.
rust ownership
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
Idiomatic Rust usessnake_casefor variables, methods, macros, and fields;UpperCamelCasefor types; andSCREAMING_SNAKE_CASEfor statics and constants. Useop_a/op_binstead, please.
– Shepmaster
Nov 22 '18 at 0:00
add a comment |
I want the code below to work, but since map() takes ownership of Option, and there doesn't seem to be a clone() function for Option, the following doesn't compile.
fn main() {
struct ItemA {
a: String,
b: String,
}
let foo = Some(ItemA {
a: "A String".to_owned(),
b: "B String".to_owned(),
});
// OR
// let foo = None;
let opA: Option<String> = foo.map(|c| c.a);
let opB: Option<String> = foo.map(|c| c.b);
}
error[E0382]: use of moved value: `foo`
--> src/main.rs:15:31
|
14 | let opA: Option<String> = foo.map(|c| c.a);
| --- value moved here
15 | let opB: Option<String> = foo.map(|c| c.b);
| ^^^ value used here after move
|
= note: move occurs because `foo` has type `std::option::Option<main::ItemA>`, which does not implement the `Copy` trait
It would be nice if opA can take ownership of ItemA.a (so it doesn't have to clone the strings), and opB can take ownership of ItemA.b
Is this possible to do without having to use if statements to check if the Option is Some or None, unwrapping, and wrapping it back up individually.
rust ownership
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
I want the code below to work, but since map() takes ownership of Option, and there doesn't seem to be a clone() function for Option, the following doesn't compile.
fn main() {
struct ItemA {
a: String,
b: String,
}
let foo = Some(ItemA {
a: "A String".to_owned(),
b: "B String".to_owned(),
});
// OR
// let foo = None;
let opA: Option<String> = foo.map(|c| c.a);
let opB: Option<String> = foo.map(|c| c.b);
}
error[E0382]: use of moved value: `foo`
--> src/main.rs:15:31
|
14 | let opA: Option<String> = foo.map(|c| c.a);
| --- value moved here
15 | let opB: Option<String> = foo.map(|c| c.b);
| ^^^ value used here after move
|
= note: move occurs because `foo` has type `std::option::Option<main::ItemA>`, which does not implement the `Copy` trait
It would be nice if opA can take ownership of ItemA.a (so it doesn't have to clone the strings), and opB can take ownership of ItemA.b
Is this possible to do without having to use if statements to check if the Option is Some or None, unwrapping, and wrapping it back up individually.
rust ownership
rust ownership
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
edited Nov 22 '18 at 0:00
Shepmaster
155k14307452
155k14307452
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
asked Nov 21 '18 at 22:57
Prime_AqasixPrime_Aqasix
510514
510514
Idiomatic Rust usessnake_casefor variables, methods, macros, and fields;UpperCamelCasefor types; andSCREAMING_SNAKE_CASEfor statics and constants. Useop_a/op_binstead, please.
– Shepmaster
Nov 22 '18 at 0:00
add a comment |
Idiomatic Rust usessnake_casefor variables, methods, macros, and fields;UpperCamelCasefor types; andSCREAMING_SNAKE_CASEfor statics and constants. Useop_a/op_binstead, please.
– Shepmaster
Nov 22 '18 at 0:00
Idiomatic Rust uses
snake_case for variables, methods, macros, and fields; UpperCamelCase for types; and SCREAMING_SNAKE_CASE for statics and constants. Use op_a / op_b instead, please.– Shepmaster
Nov 22 '18 at 0:00
Idiomatic Rust uses
snake_case for variables, methods, macros, and fields; UpperCamelCase for types; and SCREAMING_SNAKE_CASE for statics and constants. Use op_a / op_b instead, please.– Shepmaster
Nov 22 '18 at 0:00
add a comment |
2 Answers
2
active
oldest
votes
You can use map_or_else.
let (opA, opB) = foo.map_or_else(
|| (None, None),
|c| (Some(c.a), Some(c.b))
);
The first function is called if foo is None, and returns two Nones. The second function is called if foo is Some and splits the members into a tuple.
Of course, this doesn't really save you much over a simple match, and will probably be harder to follow.
let (opA, opB) = match foo {
None => (None, None),
Some(c) => (Some(c.a), Some(c.b))
};
By the way, Option does implement Clone, but it requires that the contained type implements Clone.
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
add a comment |
[T]here doesn't seem to be a
clone()function forOption[...]
That's wrong, there is, if the inner type implements clone as well. So in your case, just add #[derive(Clone)] to your struct ItemA.
Next, you can use as_ref to create an Option<&T> and then use map.
let op_a = foo.as_ref().map(|c| &c.a);
let op_b = foo.as_ref().map(|c| &c.b);
println!("{:?}", op_a);
println!("{:?}", op_b);
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
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
You can use map_or_else.
let (opA, opB) = foo.map_or_else(
|| (None, None),
|c| (Some(c.a), Some(c.b))
);
The first function is called if foo is None, and returns two Nones. The second function is called if foo is Some and splits the members into a tuple.
Of course, this doesn't really save you much over a simple match, and will probably be harder to follow.
let (opA, opB) = match foo {
None => (None, None),
Some(c) => (Some(c.a), Some(c.b))
};
By the way, Option does implement Clone, but it requires that the contained type implements Clone.
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
add a comment |
You can use map_or_else.
let (opA, opB) = foo.map_or_else(
|| (None, None),
|c| (Some(c.a), Some(c.b))
);
The first function is called if foo is None, and returns two Nones. The second function is called if foo is Some and splits the members into a tuple.
Of course, this doesn't really save you much over a simple match, and will probably be harder to follow.
let (opA, opB) = match foo {
None => (None, None),
Some(c) => (Some(c.a), Some(c.b))
};
By the way, Option does implement Clone, but it requires that the contained type implements Clone.
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
add a comment |
You can use map_or_else.
let (opA, opB) = foo.map_or_else(
|| (None, None),
|c| (Some(c.a), Some(c.b))
);
The first function is called if foo is None, and returns two Nones. The second function is called if foo is Some and splits the members into a tuple.
Of course, this doesn't really save you much over a simple match, and will probably be harder to follow.
let (opA, opB) = match foo {
None => (None, None),
Some(c) => (Some(c.a), Some(c.b))
};
By the way, Option does implement Clone, but it requires that the contained type implements Clone.
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
You can use map_or_else.
let (opA, opB) = foo.map_or_else(
|| (None, None),
|c| (Some(c.a), Some(c.b))
);
The first function is called if foo is None, and returns two Nones. The second function is called if foo is Some and splits the members into a tuple.
Of course, this doesn't really save you much over a simple match, and will probably be harder to follow.
let (opA, opB) = match foo {
None => (None, None),
Some(c) => (Some(c.a), Some(c.b))
};
By the way, Option does implement Clone, but it requires that the contained type implements Clone.
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
edited Nov 21 '18 at 23:41
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
answered Nov 21 '18 at 23:18
Benjamin LindleyBenjamin Lindley
86.1k4137227
86.1k4137227
add a comment |
add a comment |
[T]here doesn't seem to be a
clone()function forOption[...]
That's wrong, there is, if the inner type implements clone as well. So in your case, just add #[derive(Clone)] to your struct ItemA.
Next, you can use as_ref to create an Option<&T> and then use map.
let op_a = foo.as_ref().map(|c| &c.a);
let op_b = foo.as_ref().map(|c| &c.b);
println!("{:?}", op_a);
println!("{:?}", op_b);
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
add a comment |
[T]here doesn't seem to be a
clone()function forOption[...]
That's wrong, there is, if the inner type implements clone as well. So in your case, just add #[derive(Clone)] to your struct ItemA.
Next, you can use as_ref to create an Option<&T> and then use map.
let op_a = foo.as_ref().map(|c| &c.a);
let op_b = foo.as_ref().map(|c| &c.b);
println!("{:?}", op_a);
println!("{:?}", op_b);
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
add a comment |
[T]here doesn't seem to be a
clone()function forOption[...]
That's wrong, there is, if the inner type implements clone as well. So in your case, just add #[derive(Clone)] to your struct ItemA.
Next, you can use as_ref to create an Option<&T> and then use map.
let op_a = foo.as_ref().map(|c| &c.a);
let op_b = foo.as_ref().map(|c| &c.b);
println!("{:?}", op_a);
println!("{:?}", op_b);
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
[T]here doesn't seem to be a
clone()function forOption[...]
That's wrong, there is, if the inner type implements clone as well. So in your case, just add #[derive(Clone)] to your struct ItemA.
Next, you can use as_ref to create an Option<&T> and then use map.
let op_a = foo.as_ref().map(|c| &c.a);
let op_b = foo.as_ref().map(|c| &c.b);
println!("{:?}", op_a);
println!("{:?}", op_b);
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
answered Nov 22 '18 at 7:15
hellowhellow
5,19242242
5,19242242
add a comment |
add a comment |
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Idiomatic Rust uses
snake_casefor variables, methods, macros, and fields;UpperCamelCasefor types; andSCREAMING_SNAKE_CASEfor statics and constants. Useop_a/op_binstead, please.– Shepmaster
Nov 22 '18 at 0:00