Exetools - StringT functions interpretion

anybody can explain the code where I have marked, many thanks! especially I don't understand what typer of operator is using by the string operation MFC function; thanks for your help

Code:

int __cdecl sub_47D97D(int a1, int a2, int a3)

{

  int v3; // eax@1

  int v4; // eax@2

  int v5; // eax@5

  int v6; // eax@5

  int v7; // eax@6



  ((void (__thiscall *)(int, _DWORD))ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>)(

    a1,

    0);                   //what does it mean?

  v3 = 0;

  while ( a3 > 0 )

  {

    --a3;

    v4 = ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::Find(45, v3);

    if ( v4 == -1 )

      return a1;

    v3 = v4 + 1;

  }

  v5 = ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::Mid(a2, &a3, v3);

  ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::operator_(a1, v5);   //what mean?

  ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::_CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>(&a3);  //what mean?

  v6 = ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::Find(45, 0);

  if ( v6 >= 0 )

  {

    v7 = ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::Left(a1, &a3, v6);

    ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::operator_(a1, v7);  //what mean?

    ATL::CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>::_CStringT<char_StrTraitMFC_DLL<char_ATL::ChTraitsCRT<char>>>(&a3);    ////what mean?

  }

  return a1;

}