Can I create a new operator in C++ and how?

Question

MATLAB arrays support matrix operations and element operations. For example, M*N and M.*N. This is a quite intuitive way to distinguish ‎the two di

Answer 1

In C++, there's a list of predefined operators, most of which are overloadable (.* is not). Additionally, any name can be used as an operator like:

#include 

// generic LHSlt holder
template
struct LHSlt {
    LHS lhs_;
};

// declare myop as an operator-like construct
enum { myop };

// parse 'lhs 
LHSlt operator<(const LHS& lhs, decltype(myop))
{
    return { lhs };
}

// declare (int  int) -> int
int operator>(LHSlt lhsof, int rhs)
{
    int& lhs = lhsof.lhs_;
    // here comes your actual implementation
    return (lhs + rhs) * (lhs - rhs);
}

// strictly optional
#define MYOP 

int main() {
    std::cout << (5  2) << ' ' << (5 MYOP 2);
}

Disclaimer: This, strictly speaking, gets translated to (5 < myop) > 2, which is LHSlt(5) > 2. Thus it's not a new 'operator', in C++-terms, but it's used exactly the same way, even in terms of ADL. Also, if type is large, you probably want to store const T&.

Note that you can do this with any binary operator that can be defined external to the class; precedence is based on the precedence of the two sides (< and >). Thus you can have e.g. *myop*, +myop+, <>, , |myop| in this order of precedence.

If you want right-associativity, it gets a bit more tricky. You'll need both of a RHS-holder and LHS-holder (the latter being LHSlt here) and use surrounding operators such that the right one has higher precedence than the left one, e.g. a |myop> b |myop>c is a |myop> (b |myop> c). Then you need the function for both your type and your holder type as the lhs.