Re: question on map< list<T>::iterator, int>

Consider the program x.cpp :

#include <cstdlib>
#include <iostream>
#include <list>
#include <map>

using namespace std;

int main()
{
        map<list<int>::iterator, int> m;

        list<int> c;
        c.push_back(100);

        // m[c.begin()] = 10;

        return EXIT_SUCCESS;
}

This program compiles fine with the command
g++ -std=c++98 -pedantic -Wall -Wextra x.cpp

However if I remove the comment, I get compilation error because
operator '<' is not defined for list<T>::iterator. Why doesn't the
compiler give this error for
'map<list<int>::iterator, int> m;' itself. That is, in this first
statement inside main() itself, the compiler can know that the less-
than operator cannot be defined for the key type. So, why does the
compiler wait for an element to be pushed on to the map to flag the
error ?

Kindly clarify

Thanks
V.Subramanian