std::deque<T,Allocator>::emplace_front
From cppreference.com
                    
                                        
                    
                    
                                                            
                    
|   template< class... Args > void emplace_front( Args&&... args );  | 
 (since C++11)  (until C++17)  | 
|
|   template< class... Args > reference emplace_front( Args&&... args );  | 
(since C++17) | |
Inserts a new element to the beginning of the container. The element is constructed through std::allocator_traits::construct, which typically uses placement-new to construct the element in-place at the location provided by the container. The arguments args... are forwarded to the constructor as std::forward<Args>(args)....
All iterators, including the past-the-end iterator, are invalidated. No references are invalidated.
Parameters
| args | - | arguments to forward to the constructor of the element | 
| Type requirements | ||
 -T (the container's element type) must meet the requirements of EmplaceConstructible.
 | ||
Return value
| (none) | (until C++17) | 
| A reference to the inserted element. | (since C++17) | 
Complexity
Constant.
Exceptions
If an exception is thrown, this function has no effect (strong exception guarantee).
See also
|    inserts an element to the beginning  (public member function)  |