understanding std::find_if() using a lamda on std::pair

Question

It is my understanding that std::find_if() below returns an iterator to the first element in the range of arg for which the third argument (lamda function) returns true. Is that correct?

Could somebody explain why there isn't an iterator defined like this std::pair<std::string, std::type_index>::iterator = std::find_if(...) ?

Where is the iterator returned by std::find_if() stored and how can you call ->second on its own and not on an iterator?

std::type_index argType(const std::string& name) const
{
    return std::find_if(args_.begin(), args_.end(),
        [&name](std::pair<std::string, std::type_index> arg)->bool
        {
            return arg.first == name;
        }
    )->second;
}

Answer 1

It is my understanding that std::find_if() below returns an iterator

Yes, but that iterator is then dereferenced within the same expression. The function returns a copy of the std::type_index from some element of args_ , which is presumably some std-like container with a value_type of std::pair<std::string, std::type_index> (or similar).

At a guess it's a std::vector<std::pair<std::string, std::type_index>> , because if it were a map the whole function could be simplified to

return args_.at(name);

Could somebody explain why there isn't an iterator defined like this std::pair<std::string, std::type_index>::iterator = std::find_if(...) ?

Well firstly std::pair doesn't have a member iterator . I assume you meant std::vector<std::pair<std::string, std::type_index>>::iterator (or whichever collection type args_ is).

There doesn't need to be a separate statement declaring such an iterator, in much the same way as you don't need a separate double in the statement

return floor(3.14 * radius);

when you want an integer circumference calculation.

Where is the iterator returned by std::find_if() stored

Anywhere the compiler likes. It only exists while the return statement is being evaluated.

how can you call ->second on its own

You aren't. You are calling it on the temporary returned by std::find_if

and why is there a != args_.end() after the closing brace of std::find_if ?

There isn't. The author assumes that they will find a matching element. If they don't, the program has undefined behaviour. That may be intentional, or it may be a bug.