Why do I get the error “cannot infer type” when using futures::ok?
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I know there is join_all but it cannot infer type:
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
fn main()
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
println!(":?", futures::future::join_all(tasks).wait().unwrap());
I got this error:
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
----- ^^^^^^ cannot infer type for `E`
|
consider giving `tasks` a type
rust future
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
add a comment |
I know there is join_all but it cannot infer type:
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
fn main()
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
println!(":?", futures::future::join_all(tasks).wait().unwrap());
I got this error:
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
----- ^^^^^^ cannot infer type for `E`
|
consider giving `tasks` a type
rust future
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
Have you consider to consider givingtasksa type ?let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)];orlet tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
– Stargateur
Nov 15 '18 at 13:34
add a comment |
I know there is join_all but it cannot infer type:
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
fn main()
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
println!(":?", futures::future::join_all(tasks).wait().unwrap());
I got this error:
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
----- ^^^^^^ cannot infer type for `E`
|
consider giving `tasks` a type
rust future
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
I know there is join_all but it cannot infer type:
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
fn main()
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
println!(":?", futures::future::join_all(tasks).wait().unwrap());
I got this error:
let tasks = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
----- ^^^^^^ cannot infer type for `E`
|
consider giving `tasks` a type
rust future
rust future
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
edited Nov 16 '18 at 2:05
Shepmaster
162k16333477
162k16333477
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
asked Nov 15 '18 at 13:09
rofrolrofrol
7,92534649
7,92534649
Have you consider to consider givingtasksa type ?let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)];orlet tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
– Stargateur
Nov 15 '18 at 13:34
add a comment |
Have you consider to consider givingtasksa type ?let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)];orlet tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
– Stargateur
Nov 15 '18 at 13:34
Have you consider to consider giving
tasks a type ? let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)]; or let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];– Stargateur
Nov 15 '18 at 13:34
Have you consider to consider giving
tasks a type ? let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)]; or let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];– Stargateur
Nov 15 '18 at 13:34
add a comment |
2 Answers
2
active
oldest
votes
The problem is that any future may in theory return an error. So the FutureResult type (which is returned from fut_ok) is generic with two type parameters: a type T for success and a type E for errors.
If this was real code instead of a toy example, you would have some error handling code that would allow the compiler to infer type E. In this case you need to specify it, but since you don't use it you can use the empty type (). So either of the following should work:
let tasks: Vec<FutureResult<_, ()>> = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
or
let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
Note that the first is what the compiler means when it says: "consider giving tasks a type".
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
nice. And how to print the result?println!(":?", futures::future::join_all(tasks).wait()?);the traitstd::error::Erroris not implemented for()
– rofrol
Nov 15 '18 at 13:38
add a comment |
Full example
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
use futures::future::FutureResult;
fn main() _
Prints Ok([1, 2, 3])
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
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
The problem is that any future may in theory return an error. So the FutureResult type (which is returned from fut_ok) is generic with two type parameters: a type T for success and a type E for errors.
If this was real code instead of a toy example, you would have some error handling code that would allow the compiler to infer type E. In this case you need to specify it, but since you don't use it you can use the empty type (). So either of the following should work:
let tasks: Vec<FutureResult<_, ()>> = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
or
let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
Note that the first is what the compiler means when it says: "consider giving tasks a type".
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
nice. And how to print the result?println!(":?", futures::future::join_all(tasks).wait()?);the traitstd::error::Erroris not implemented for()
– rofrol
Nov 15 '18 at 13:38
add a comment |
The problem is that any future may in theory return an error. So the FutureResult type (which is returned from fut_ok) is generic with two type parameters: a type T for success and a type E for errors.
If this was real code instead of a toy example, you would have some error handling code that would allow the compiler to infer type E. In this case you need to specify it, but since you don't use it you can use the empty type (). So either of the following should work:
let tasks: Vec<FutureResult<_, ()>> = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
or
let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
Note that the first is what the compiler means when it says: "consider giving tasks a type".
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
nice. And how to print the result?println!(":?", futures::future::join_all(tasks).wait()?);the traitstd::error::Erroris not implemented for()
– rofrol
Nov 15 '18 at 13:38
add a comment |
The problem is that any future may in theory return an error. So the FutureResult type (which is returned from fut_ok) is generic with two type parameters: a type T for success and a type E for errors.
If this was real code instead of a toy example, you would have some error handling code that would allow the compiler to infer type E. In this case you need to specify it, but since you don't use it you can use the empty type (). So either of the following should work:
let tasks: Vec<FutureResult<_, ()>> = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
or
let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
Note that the first is what the compiler means when it says: "consider giving tasks a type".
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
The problem is that any future may in theory return an error. So the FutureResult type (which is returned from fut_ok) is generic with two type parameters: a type T for success and a type E for errors.
If this was real code instead of a toy example, you would have some error handling code that would allow the compiler to infer type E. In this case you need to specify it, but since you don't use it you can use the empty type (). So either of the following should work:
let tasks: Vec<FutureResult<_, ()>> = vec![fut_ok(1), fut_ok(2), fut_ok(3)];
or
let tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];
Note that the first is what the compiler means when it says: "consider giving tasks a type".
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
answered Nov 15 '18 at 13:34
JmbJmb
2,960525
2,960525
nice. And how to print the result?println!(":?", futures::future::join_all(tasks).wait()?);the traitstd::error::Erroris not implemented for()
– rofrol
Nov 15 '18 at 13:38
add a comment |
nice. And how to print the result?println!(":?", futures::future::join_all(tasks).wait()?);the traitstd::error::Erroris not implemented for()
– rofrol
Nov 15 '18 at 13:38
nice. And how to print the result?
println!(":?", futures::future::join_all(tasks).wait()?); the trait std::error::Error is not implemented for ()– rofrol
Nov 15 '18 at 13:38
nice. And how to print the result?
println!(":?", futures::future::join_all(tasks).wait()?); the trait std::error::Error is not implemented for ()– rofrol
Nov 15 '18 at 13:38
add a comment |
Full example
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
use futures::future::FutureResult;
fn main() _
Prints Ok([1, 2, 3])
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
add a comment |
Full example
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
use futures::future::FutureResult;
fn main() _
Prints Ok([1, 2, 3])
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
add a comment |
Full example
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
use futures::future::FutureResult;
fn main() _
Prints Ok([1, 2, 3])
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
Full example
extern crate futures; // 0.1.25
use futures::future::ok as fut_ok;
use futures::future::FutureResult;
fn main() _
Prints Ok([1, 2, 3])
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
answered Nov 15 '18 at 15:20
rofrolrofrol
7,92534649
7,92534649
add a comment |
add a comment |
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Have you consider to consider giving
tasksa type ?let tasks : Vec<FutureResult<_, ()>> = vec![fut_ok(1u32), fut_ok(2), fut_ok(3)];orlet tasks = vec![fut_ok::<_, ()>(1), fut_ok(2), fut_ok(3)];– Stargateur
Nov 15 '18 at 13:34