Question

From language design point of view , What type of practice is supporting operator overloading?

What are the pros & cons (if any) ?

Answer 1

EDIT: it has been mentioned that std::complex is a much better example than std::string for “good use” of operator overloading, so I am including an example of that as well:

std::complex<double> c;
c = 10.0;
c += 2.0;
c = std::complex<double>(10.0, 1.0);
c = c + 10.0;

Aside from the constructor syntax, it looks and acts just like any other built in type.

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The primary pro is that you can create new types which act like the built in types. A good example of this is std::string (see above for a better example) in c++. Which is implemented in the library and is not a basic type. Yet you can write things like:

std::string s = "hello"
s += " world";
if(s == "hello world") {
    //....
}

The downside is that it is easy to abuse. Poor choices in operator overloading can lead to accidentally inefficient or unclear code. Imagine if std::list had an operator[]. You may be tempted to write:

for(int i = 0; i < l.size(); ++i) {
    l[i] += 10;
}

that’s an O(n^2) algorithm! Ouch. Fortunately, std::list does not have operator[] since it is assumed to be an efficient operation.