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Why are len() and is_empty() not defined in a trait?


By : swapna
Date : August 01 2020, 06:00 AM
this one helps. Most patterns in Rust are captured by traits (Iterator, From, Borrow, etc.). ,
Was it deemed useless?
code :


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Trying to create and use a class; name 'is_empty' is not defined


By : hiyuux
Date : March 29 2020, 07:55 AM
To fix the issue you can do The method is_empty() is part of the class. To call it you need to my_stack.is_empty()

Do I have to 'use' a trait in order to call methods defined in that trait?


By : Yara Ismail
Date : March 29 2020, 07:55 AM
will help you You're thinking of traits in terms of inheritance. It might make more sense if you think of a trait as a module that's overloadable with respect to the Self type. From this perspective, it makes sense that the trait has to be in scope in order for the compiler to know about its methods, just as a module has to be in scope in order to use it. A particular implication of this is that implementations can be declared alongside the trait they implement rather than the type they implement it for. In this situation, clearly if your code doesn't know about the trait, it can't use its methods.
Another motivation for the current behaviour is that multiple traits can define methods with the same name, and when you have such a conflict for traits implemented for the same type, you can no longer use method call syntax to access their methods. Instead, you have to use function call syntax in order to specify which trait the method is a member of (the trait acting as the module the method is in). If method call syntax used all traits in your program rather than just the ones in scope for method resolution, you'd end up with these conflicts much more often, since you'd have name conflicts with methods in traits that your code isn't actually using directly.

if a variable is defined in a class extends a trait, how to use it in the trait?


By : Ali
Date : March 29 2020, 07:55 AM
like below fixes the issue I have the following code, T1 need to access "a" which is the constructor parameter of Test (extends T1), but compile failed. How to fix it? , There are several possibilities:

Trait implementation for both a trait object and for direct implementors of the trait


By : Cop3Tx
Date : March 29 2020, 07:55 AM
around this issue Implement your trait for all Box where S implements your trait. Then you simply delegate to the existing implementation:
code :
impl<S: Solid + ?Sized> Solid for Box<S> {
    fn intersect(&self, ray: f32) -> f32 {
        (**self).intersect(ray)
    }
}
impl<'a, S: Solid + ?Sized> Solid for &'a S {
    fn intersect(&self, ray: f32) -> f32 {
        (**self).intersect(ray)
    }
}
trait Solid {
    fn intersect(&self, ray: f32) -> f32;
}

impl<S: Solid + ?Sized> Solid for Box<S> {
    fn intersect(&self, ray: f32) -> f32 {
        (**self).intersect(ray)
    }
}

impl<'a, S: Solid + ?Sized> Solid for &'a S {
    fn intersect(&self, ray: f32) -> f32 {
        (**self).intersect(ray)
    }
}

struct Group<S>(Vec<S>);

impl<S: Solid> Solid for Group<S> {
    fn intersect(&self, ray: f32) -> f32 {
        42.42
    }
}

struct Point;

impl Solid for Point {
    fn intersect(&self, ray: f32) -> f32 {
        100.
    }
}

fn main() {
    let direct = Group(vec![Point]);
    let boxed = Group(vec![Box::new(Point)]);
    let pt = Point;
    let reference = Group(vec![&pt]);

    let mixed: Group<Box<Solid>> = Group(vec![
        Box::new(direct),
        Box::new(boxed),
        Box::new(Point),
        Box::new(reference),
    ]);

    mixed.intersect(1.0);
}

Why is the trait bound Trait<&String> not satisfied even though I've implemented Trait<&str>?


By : Jonty
Date : March 29 2020, 07:55 AM
I wish this help you I have written the following code: ,
How can I fix this?
code :
let binary_string = self.to_binary(&*data);
fn main() {
    let mut s = Serializer;
    let a: String = "a".to_string();
    // autoderef &String to &str and call Serialize<&str>::to_bert()
    // I don't know why the autoderef does not work in your original example
    s.to_bert(&a);
}
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