编译器可以对trait的方法进行默认实现的内联吗?

如果我理解正确的话,你问的是两件事:

• magnitude ?
• square_magnitude 里面 震级 它本身是声明的 inline 平方μ震级

disassembly :

trait Magnitude {
    fn square_magnitude( &self ) -> f64;

    #[inline]
    fn magnitude( &self ) -> f64 {
        self.square_magnitude().sqrt()
    }
}

struct Vector { x: f64, y: f64 }

impl Magnitude for Vector {
    #[inline]
    fn square_magnitude (&self) -> f64 {
        self.x*self.x + self.y*self.y
    }
}

pub fn test (x: f64, y: f64) -> f64 {
    let v = Vector { x: x, y: y };
    v.magnitude()
}

用rustcv1.28.0和option编译 -O

example::test:
        mulsd   xmm0, xmm0
        mulsd   xmm1, xmm1
        addsd   xmm1, xmm0
        xorps   xmm0, xmm0
        sqrtsd  xmm0, xmm1
        ret

但是请注意 compiler will not inline square_magnitude inside magnitude if square_magnitude is not declared inline itself :

impl Magnitude for Vector {
    fn square_magnitude (&self) -> f64 {
        self.x*self.x + self.y*self.y
    }
}

<example::Vector as example::Magnitude>::square_magnitude:
        movsd   xmm1, qword ptr [rdi]
        movsd   xmm0, qword ptr [rdi + 8]
        mulsd   xmm1, xmm1
        mulsd   xmm0, xmm0
        addsd   xmm0, xmm1
        ret

example::test:
        mulsd   xmm0, xmm0
        mulsd   xmm1, xmm1
        addsd   xmm1, xmm0
        xorps   xmm0, xmm0
        sqrtsd  xmm0, xmm1
        ret