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#include <iostream>
#include <utility> // for std::pair

int main()
{
    std::pair<int, char> my_pair(1, 'a');
    std::cout << my_pair.first << " : " << my_pair.second << std::endl;
}

              
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#include <iostream>
#include <utility> // for std::pair

int main()
{
    std::pair<> my_pair(1, 'a'); // Error
    std::cout << my_pair.first << " : " << my_pair.second << std::endl;
}

              
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#include <iostream>

template <typename T>
class Box {
    T value;
public:
    Box(T value): value(value) {}
};

int main()
{
	// No need to write Box<int> a{1};
    Box a{1}; // Deduction: Box<int>
    Box b{a}; // Deduction: Box<int>, not Box<Box<int>>
}

              
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template <typename T>
class Vector3D {
    T x, y, z;
public:
    Vector3D(T x, T y, T z) : x(x), y(y), z(z) {}
};

Vector3D vec{1.0, 2.0, 3.0}; // CTAD deduces Vector3D<double>