Supporting mock with methods that return an object with a generic lifetime?

[Galgamins]

Currently, you cannot use mockall to mock a method with a lifetime parameter where that lifetime is also part of the return type.

For example

pub struct MyStruct<'a>{
    test: &'a u8
}

impl<'a> MyStruct<'a>{
    pub fn create() -> MyStruct<'a>{
        MyStruct{
            test : &0
        }
    }
}

If you try to automock this you get an error use of undeclared lifetime name 'a

Is this something that can be supported in the future, or is this completely impossible to support?

[asomers]

It looks like you're trying to mock a constructor. The Expectation for a constructor must inherently be 'static, since it isn't associated with any mock object. That means that the returning closure can't capture any non-'static data. So the best you can do would be to use mock! instead of #[automock], and define the mock object's constructor to always return a static struct, like this:

mock! {
    pub struct MyStruct<'a> {
        pub fn create() -> MyStruct<'static>;
    }
}

[Galgamins]

Thanks for the suggestion!

When I do this

mock! {
    pub struct MyStruct<'a> {
        pub fn create() -> MyStruct<'static>;
    }
}

I get a compile error that highlights struct and says the compiler expected a identifier. Any idea what causes that?

[asomers]

No, not if you don't paste in the error.

[Galgamins]

test.rs

mock! {

    pub static struct MyStruct<'a> {

        pun fm create() -> MyStruct<'static>;

    }

}

error: expected identifier

  --> test.rs:16:9

   |

16 |     pub static struct MyStruct<'a> {

   |         ^^^^^^

 error: could not compile `test` due to previous error

[asomers]

Why did you put that static in between pub and struct? Are you forgetting that you aren't using C++ anymore?

[Galgamins]

Ah oops, yes I did. Though funny enough the same issue happens without the static.

mock! {

    pub struct MyStruct<'a> {

        pub fm create() -> MyStruct<'static>;

    }

}

error: expected identifier

  --> test.rs:16:9

   |

16 |     pub struct MyStruct<'a> {

   |         ^^^^^^

 error: could not compile `test` due to previous error

[asomers]

Now get rid of the "struct", like the error suggests.

[Galgamins]

Thanks, that solved the problem!