How to call associated function?

help
#1

I want to write a struct which has a take function and also implements the Iterator trait. How can I call the take associated function instead of the trait function? The compiler calls the take of the Iterator trait. How it works? The Option type also has a take as associated function and implements iterator, but it call associated function when I write option.take()

pub struct Wrapper<T> {
    inner: Vec<T>,
}

impl<T> Wrapper<T> {
    pub fn take(&mut self) -> Option<T> {
        self.inner.pop()
    }
}

impl<T> Iterator for Wrapper<T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        Self::take(self)
    }
}

fn main() {
    let mut wrapper = Wrapper {
        inner: vec![],
    };
    
    let _ = wrapper.take();
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
error[E0061]: this function takes 1 argument but 0 arguments were supplied
    --> src/main.rs:24:21
     |
24   |     let _ = wrapper.take();
     |                     ^^^^- supplied 0 arguments
     |                     |
     |                     expected 1 argument
     |
note: associated function defined here

For more information about this error, try `rustc --explain E0061`.
error: could not compile `playground` due to previous error
#2

You can use the fully-qualified syntax to call it:

fn main() {
    let mut wrapper: Wrapper<String> = Wrapper {
        inner: vec![],
    };
    
    let _ = Wrapper::take(&mut wrapper);
}
#3

I can, but I thought an associated function should be in priority :face_with_raised_eyebrow:
I tested it with this example:

#4

It looks I get what the problem is. The Option type implements the IntoIterator but not the Iterator. This allows you to call take

#5

Inherent method has priority over trait method, yes, but (self) method takes priority over (&mut self) method when called on an owned value. You could use (&mut wrapper).take() to call the inherent method instead.

Your observation about why the problem doesn't appear for the Option type is still accurate :wink:

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