TIL: C++17 can do variable initialization inside `if` conditions

This is a totally valid C++ program:

if (auto it = m.find(10); it != m.end())
    return it->second.size();

Note the two parts of the if condition separated by a ;. The first part initializes the variable, and is the actual condition to be checked.

Benefits include limiting the scope of the initialized variable to the if body.

This has interesting implications when used with RAII:

if (std::lock_guard lock(mx); shared_flag) {
    unsafe_ping();
    shared_flag = false;
}

The above code ensures the mutex mx is only locked for the body of the if.

(code snippets taken from documentation)

Source: Saw this feature used in the wild during my internship at AWS Redshift.