What is an elvis operator?

Question

I have heard so much about this operator but didn't know the best use cases.

Answer 1

the Elvis operator ?: is a binary operator that returns its first operand if that operand is true, and otherwise evaluates and returns its second operand.

In a language that supports the Elvis operator, something like this:

x = f() ?: g()

will set x equal to the result of f() if that result is a true value, and to the result of g() otherwise.

It is equivalent to this example, using the Ternary Operator:

x = f() ? f() : g()

except that it does not evaluate the f() twice if it is true.

Credit:Wiki