vector<>::clear() problem with const data member

[iammilind]

In one of my code, I was using vector<> for certain class. In one of my struct, I have 'const' member data. However, vector<>::clear() throws compile error with that:
===========================================
struct Test
{
const string Str;
Test(const string str) : Str(str)
{}
};

struct TestWrapper
{
vector<Test> vObj;
~TestWrapper()
{
// vObj.clear(); // If you remove above comment, it gives following error
} // However, it works fine with vObj.pop_back()
};

Error:
/usr/lib/gcc/x86_64-redhat-linux/3.4.6/../../../../include/c++/3.4.6/bits/stl_algobase.h: In member function `Test& Test::operator=(const Test&)':
...
/usr/lib/gcc/x86_64-redhat-linux/3.4.6/../../../../include/c++/3.4.6/bits/stl_algobase.h:247: error: non-static const member `const std::string Test::Str', can't use default assignment operator ===========================================


My confusion is why in the 1st place vector<>::clear() should require to use operator =() of class ? Should not it be as easy as pop_back() ?
(if I overload the assignment and copy constructor, it doesn't give error and works fine.
Thanks & happy new year !

[newb16]

My guess is than since vector requires containing objects to be copyable, it doesn't matter that some functions compile and some doesn't if this condition isn't met - it depends on internal implementation.