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First part :
std::initializer_list is a really helpful feature of C++11, so I wondered how it is implemented in the standard library. From what I read here, the compiler creates an array of type T and gives the pointer to the initializer_list<T>.
It also states that copying an initializer_list will create a new object referencing the same data : why is it so ? I would have guessed that it either :
initializer_list
initializer_list
Second part :
From just one of many online references for the std::vector constructors:
vector (initializer_list<value_type> il,
const allocator_type& alloc = allocator_type());
(6) initializer list constructor
Constructs a container with a copy of each of the elements in il, in the same order.
I am not comfortable with move semantics yet, but couldn't the data of il be moved to the vector ? I am not aware of the deep implementation of std::vector but IIRC it uses plain-old arrays.
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An object of type std::initializer_list<T> is a lightweight proxy object that provides access to an array of objects of type const T .
Initializer List is used in initializing the data members of a class. The list of members to be initialized is indicated with constructor as a comma-separated list followed by a colon. Following is an example that uses the initializer list to initialize x and y of Point class.
Uniform initialization is a feature in C++ 11 that allows the usage of a consistent syntax to initialize variables and objects ranging from primitive type to aggregates. In other words, it introduces brace-initialization that uses braces ({}) to enclose initializer values.
What is the underlying structure of
std::initializer_list?
Most likely, just a pair of pointers, or a pointer and a size. Paragraph 18.9/2 of the C++11 Standard even mentions this in a (non-normative) note:
An object of type
initializer_list<E>provides access to an array of objects of typeconst E. [ Note: A pair of pointers or a pointer plus a length would be obvious representations forinitializer_list.initializer_listis used to implement initializer lists as specified in 8.5.4. Copying aninitializer listdoes not copy the underlying elements. —end note ]
Moreover:
I am not comfortable with move semantics yet, but couldn't the data of
ilbe moved to the vector?
No, you can't move from the elements of an initializer_list, since elements of an initializer_list are supposed to be immutable (see the first sentence of the paragraph quoted above). That's also the reason why only const-qualified member functions give you access to the elements.
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