Hello,
I have a type that requires a rather long set of bounds. As such, I have created an empty trait that recalls all the used bounds. I then use the trat anywhere I need those bounds.
The problem now is that I need some bounds on the reference type of the trait.
Here is a code that exemplifies the situation. I want function func working without the for<'a> ... bounds. Is that possible somehow?
use num::{Zero, Signed, Num};
use std::ops::{Add, AddAssign, Div, Mul, Sub, SubAssign};
trait Elem: // Make sure R::Elem is Self
Zero
+ Clone
+ Signed
+ Add<Self, Output = Self>
+ AddAssign
+ Sub<Self, Output = Self>
+ SubAssign
+ Mul<Self, Output = Self>
+ Div<Self, Output = Self>
+ Num
+ Sync
+ Send
+ Sized
where
for<'a> &'a Self: Add<&'a Self, Output = Self>
+ Sub<&'a Self, Output = Self>
+ Mul<&'a Self, Output = Self>
+ Div<&'a Self, Output = Self>
{
}
fn func<R>(a: R)
where
R: Elem + std::fmt::Debug,
// ==========>>> uncommenting the next lines solves the errors! <<<===========
// for<'a> &'a R: Add<&'a R, Output = R>
// + Sub<&'a R, Output = R>
// + Mul<&'a R, Output = R>
// + Div<&'a R, Output = R>,
{
println!("{:?}", a);
}
impl Elem for i32 {}
fn main()
{
func(5);
}
Errors:
Compiling playground v0.0.1 (/playground)
error[E0277]: cannot add `&'a R` to `&'a R`
--> src/main.rs:30:8
|
30 | R: Elem + std::fmt::Debug,
| ^^^^ no implementation for `&'a R + &'a R`
|
= help: the trait `for<'a> Add` is not implemented for `&'a R`
note: required by a bound in `Elem`
--> src/main.rs:20:27
|
5 | trait Elem: // Make sure R::Elem is Self
| ---- required by a bound in this trait
...
20 | for<'a> &'a Self: Add<&'a Self, Output = Self>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Elem`
help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
|
30 | R: Elem + std::fmt::Debug, for<'a> &'a R: Add
| ~~~~~~~~~~~~~~~~~~~~
error[E0277]: cannot subtract `&'a R` from `&'a R`
--> src/main.rs:30:8
|
30 | R: Elem + std::fmt::Debug,
| ^^^^ no implementation for `&'a R - &'a R`
|
= help: the trait `for<'a> Sub` is not implemented for `&'a R`
note: required by a bound in `Elem`
--> src/main.rs:21:15
|
5 | trait Elem: // Make sure R::Elem is Self
| ---- required by a bound in this trait
...
21 | + Sub<&'a Self, Output = Self>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Elem`
help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
|
30 | R: Elem + std::fmt::Debug, for<'a> &'a R: Sub
| ~~~~~~~~~~~~~~~~~~~~
error[E0277]: cannot multiply `&'a R` by `&'a R`
--> src/main.rs:30:8
|
30 | R: Elem + std::fmt::Debug,
| ^^^^ no implementation for `&'a R * &'a R`
|
= help: the trait `for<'a> Mul` is not implemented for `&'a R`
note: required by a bound in `Elem`
--> src/main.rs:22:15
|
5 | trait Elem: // Make sure R::Elem is Self
| ---- required by a bound in this trait
...
22 | + Mul<&'a Self, Output = Self>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Elem`
help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
|
30 | R: Elem + std::fmt::Debug, for<'a> &'a R: Mul
| ~~~~~~~~~~~~~~~~~~~~
error[E0277]: cannot divide `&'a R` by `&'a R`
--> src/main.rs:30:8
|
30 | R: Elem + std::fmt::Debug,
| ^^^^ no implementation for `&'a R / &'a R`
|
= help: the trait `for<'a> Div` is not implemented for `&'a R`
note: required by a bound in `Elem`
--> src/main.rs:23:15
|
5 | trait Elem: // Make sure R::Elem is Self
| ---- required by a bound in this trait
...
23 | + Div<&'a Self, Output = Self>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Elem`
help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
|
30 | R: Elem + std::fmt::Debug, for<'a> &'a R: Div
| ~~~~~~~~~~~~~~~~~~~~
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (bin "playground") due to 4 previous errors