explicit forward_list(const Allocator&);
Effects: Constructs an empty forward_list object using the specified allocator.
Complexity: Constant.
explicit forward_list(size_type n, const Allocator& = Allocator());
Effects: Constructs a forward_list object with n default-inserted elements using the specified allocator.
Requires: T shall be DefaultInsertable into *this.
Complexity: Linear in n.
forward_list(size_type n, const T& value, const Allocator& = Allocator());
Effects: Constructs a forward_list object with n copies of value using the specified allocator.
Requires: T shall be CopyInsertable into *this.
Complexity: Linear in n.
template <class InputIterator>
forward_list(InputIterator first, InputIterator last, const Allocator& = Allocator());
Effects: Constructs a forward_list object equal to the range [first, last).
Complexity: Linear in distance(first, last).