code: function (member) {
          var name = member.getName(),
              existing;
          this._checkOwnMemberDoesntExist(name);
          existing = this._members[name];
          if (existing) {
              existing.checkOverloadedWith(member);
          }
      }
docs: Before adding a member:
  - Check that it does not already exist for this class definition
  - If overloading an inherited member, check that it is compatible
  
  @param {_GpfClassDefMember} member Member to check
  @throws {gpf.Error.ClassMemberAlreadyExist}