Cannot borrow as immutable because it is also borrowed as mutable when verifing that a closure was called
I have a function that takes a closure to perform output-related logic (e.g. display to stdout):
fn handle(mut output: impl FnMut(String) -> ()) -> Result<(), String> {
// do something that produces output string `message`
let message = "example".to_string();
Ok(output(message))
}
I'm trying to write an integration test for this function, where I define a stub output function, which saves the output string to local mutable variable:
#[test]
fn should_work() {
let mut output_message = String::from("");
let output = |message: String| {
output_message = message;
};
let result = handle(output);
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
However I have error:
error[E0502]: cannot borrow `output_message` as immutable because it is also borrowed as mutable
--> src/lib.rs:18:24
|
11 | let output = |message: String| {
| ----------------- mutable borrow occurs here
12 | output_message = message;
| -------------- previous borrow occurs due to use of `output_message` in closure
...
18 | assert_eq!("blah", output_message);
| ^^^^^^^^^^^^^^ immutable borrow occurs here
19 | }
| - mutable borrow ends here
Is there any way I can test using this approach? I briefly searched for some mock crates but all of the crates don't seem to be updated very often and they are a bit overkill for my scenario anyway.
If not, any better alternative to test this function?
testing rust integration-testing
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
add a comment |
I have a function that takes a closure to perform output-related logic (e.g. display to stdout):
fn handle(mut output: impl FnMut(String) -> ()) -> Result<(), String> {
// do something that produces output string `message`
let message = "example".to_string();
Ok(output(message))
}
I'm trying to write an integration test for this function, where I define a stub output function, which saves the output string to local mutable variable:
#[test]
fn should_work() {
let mut output_message = String::from("");
let output = |message: String| {
output_message = message;
};
let result = handle(output);
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
However I have error:
error[E0502]: cannot borrow `output_message` as immutable because it is also borrowed as mutable
--> src/lib.rs:18:24
|
11 | let output = |message: String| {
| ----------------- mutable borrow occurs here
12 | output_message = message;
| -------------- previous borrow occurs due to use of `output_message` in closure
...
18 | assert_eq!("blah", output_message);
| ^^^^^^^^^^^^^^ immutable borrow occurs here
19 | }
| - mutable borrow ends here
Is there any way I can test using this approach? I briefly searched for some mock crates but all of the crates don't seem to be updated very often and they are a bit overkill for my scenario anyway.
If not, any better alternative to test this function?
testing rust integration-testing
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
2
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22
add a comment |
I have a function that takes a closure to perform output-related logic (e.g. display to stdout):
fn handle(mut output: impl FnMut(String) -> ()) -> Result<(), String> {
// do something that produces output string `message`
let message = "example".to_string();
Ok(output(message))
}
I'm trying to write an integration test for this function, where I define a stub output function, which saves the output string to local mutable variable:
#[test]
fn should_work() {
let mut output_message = String::from("");
let output = |message: String| {
output_message = message;
};
let result = handle(output);
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
However I have error:
error[E0502]: cannot borrow `output_message` as immutable because it is also borrowed as mutable
--> src/lib.rs:18:24
|
11 | let output = |message: String| {
| ----------------- mutable borrow occurs here
12 | output_message = message;
| -------------- previous borrow occurs due to use of `output_message` in closure
...
18 | assert_eq!("blah", output_message);
| ^^^^^^^^^^^^^^ immutable borrow occurs here
19 | }
| - mutable borrow ends here
Is there any way I can test using this approach? I briefly searched for some mock crates but all of the crates don't seem to be updated very often and they are a bit overkill for my scenario anyway.
If not, any better alternative to test this function?
testing rust integration-testing
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
I have a function that takes a closure to perform output-related logic (e.g. display to stdout):
fn handle(mut output: impl FnMut(String) -> ()) -> Result<(), String> {
// do something that produces output string `message`
let message = "example".to_string();
Ok(output(message))
}
I'm trying to write an integration test for this function, where I define a stub output function, which saves the output string to local mutable variable:
#[test]
fn should_work() {
let mut output_message = String::from("");
let output = |message: String| {
output_message = message;
};
let result = handle(output);
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
However I have error:
error[E0502]: cannot borrow `output_message` as immutable because it is also borrowed as mutable
--> src/lib.rs:18:24
|
11 | let output = |message: String| {
| ----------------- mutable borrow occurs here
12 | output_message = message;
| -------------- previous borrow occurs due to use of `output_message` in closure
...
18 | assert_eq!("blah", output_message);
| ^^^^^^^^^^^^^^ immutable borrow occurs here
19 | }
| - mutable borrow ends here
Is there any way I can test using this approach? I briefly searched for some mock crates but all of the crates don't seem to be updated very often and they are a bit overkill for my scenario anyway.
If not, any better alternative to test this function?
testing rust integration-testing
testing rust integration-testing
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
edited Nov 15 '18 at 15:43
Shepmaster
154k14306446
154k14306446
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
asked Nov 14 '18 at 16:10
Phuong NguyenPhuong Nguyen
2,2251717
2,2251717
2
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22
add a comment |
2
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22
2
2
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22
add a comment |
2 Answers
2
active
oldest
votes
You can put the anonymous function in a local scope, so that it is dropped by the time you assert:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = {
let output = |message: String| {
output_message = message;
};
handle(output)
};
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
add a comment |
Inline the closure:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = handle(|message| {
output_message = message;
});
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
This way, the closure is a temporary and doesn't borrow the value for a long time. As a bonus, you can avoid the type specification on the closure argument.
Or wait a few weeks until Rust 1.31 and turn on Rust 2018 mode, which has non-lexical lifetimes.
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
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 put the anonymous function in a local scope, so that it is dropped by the time you assert:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = {
let output = |message: String| {
output_message = message;
};
handle(output)
};
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
add a comment |
You can put the anonymous function in a local scope, so that it is dropped by the time you assert:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = {
let output = |message: String| {
output_message = message;
};
handle(output)
};
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
add a comment |
You can put the anonymous function in a local scope, so that it is dropped by the time you assert:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = {
let output = |message: String| {
output_message = message;
};
handle(output)
};
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
You can put the anonymous function in a local scope, so that it is dropped by the time you assert:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = {
let output = |message: String| {
output_message = message;
};
handle(output)
};
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
answered Nov 14 '18 at 16:17
TarmilTarmil
8,4132232
8,4132232
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
add a comment |
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
thanks a lot, works like a charm
– Phuong Nguyen
Nov 14 '18 at 23:24
add a comment |
Inline the closure:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = handle(|message| {
output_message = message;
});
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
This way, the closure is a temporary and doesn't borrow the value for a long time. As a bonus, you can avoid the type specification on the closure argument.
Or wait a few weeks until Rust 1.31 and turn on Rust 2018 mode, which has non-lexical lifetimes.
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
add a comment |
Inline the closure:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = handle(|message| {
output_message = message;
});
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
This way, the closure is a temporary and doesn't borrow the value for a long time. As a bonus, you can avoid the type specification on the closure argument.
Or wait a few weeks until Rust 1.31 and turn on Rust 2018 mode, which has non-lexical lifetimes.
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
add a comment |
Inline the closure:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = handle(|message| {
output_message = message;
});
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
This way, the closure is a temporary and doesn't borrow the value for a long time. As a bonus, you can avoid the type specification on the closure argument.
Or wait a few weeks until Rust 1.31 and turn on Rust 2018 mode, which has non-lexical lifetimes.
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
Inline the closure:
#[test]
fn should_work() {
let mut output_message = String::from("");
let result = handle(|message| {
output_message = message;
});
assert!(result.is_ok());
assert_eq!("blah", output_message);
}
This way, the closure is a temporary and doesn't borrow the value for a long time. As a bonus, you can avoid the type specification on the closure argument.
Or wait a few weeks until Rust 1.31 and turn on Rust 2018 mode, which has non-lexical lifetimes.
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
answered Nov 15 '18 at 15:42
ShepmasterShepmaster
154k14306446
154k14306446
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
add a comment |
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
thanks a lot. Coincidentally I also just saw your answer on sharing test utilities: stackoverflow.com/a/44545091/1273147
– Phuong Nguyen
Nov 16 '18 at 1:10
add a comment |
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2
For what it's worth, your code works without any changes when enabling non-lexical lifetimes.
– Sven Marnach
Nov 14 '18 at 19:16
@SvenMarnach interesting, I don't know about that
– Phuong Nguyen
Nov 14 '18 at 23:22