Copy elision for pass-by-value arguments

Question

Given

struct Range{
    Range(double from, double to) : from(from), to(to) {}
    double from;
    double to;
};

struct Box{
    Box(Range x, Range y) : x(x         


        

Answer 1

It should, but I fail to make it work (live example). The compiler may detect the side-effect of the constructors and decide not to go with copy elision.

#include 

struct Range{
    Range(double from, double to) : from(from), to(to) { std::cout << "Range(double,double)" << std::endl; }
    Range(const Range& other) : from(other.from), to(other.to) { std::cout << "Range(const Range&)" << std::endl; }
    double from;
    double to;
};

struct Box{
    Box(Range x, Range y) : x(x), y(y) { std::cout << "Box(Range,Range)" << std::endl; }
    Box(const Box& other) : x(other.x), y(other.y) { std::cout << "Box(const Box&)" << std::endl; }
    Range x;
    Range y;
};


int main(int argc, char** argv)
{
    (void) argv;
    const Box box(Range(argc, 1.0), Range(0.0, 2.0));
    std::cout << box.x.from << std::endl;
    return 0;
}

Compile & run:

clang++ -std=c++14 -O3 -Wall -Wextra -pedantic -Werror -pthread main.cpp && ./a.out

Output:

Range(double,double)
Range(double,double)
Range(const Range&)
Range(const Range&)
Box(Range,Range)
1