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How are variadic templates used in aggregate initialization?


Asked by Tru Harding on Dec 05, 2021 FAQ



Variadic templates ( parameter packs) have been in the language ever since C++11. With the introduction of fold expressions in C++17, they have gotten even more useful. This post showcases their utility for initializing aggregate types such as std::array without prior default initialization of their fields.
Also Know,
Variadic templates can also be used to create functions that take variable number of arguments. They are often the better choice because they do not impose restrictions on the types of the arguments, do not perform integral and floating-point promotions, and are type safe.
Similarly, It is a form of list-initialization (since C++11) or direct initialization (since C++20) An aggregate is one of the following types: array type. class type (typically, struct or union), that has. no private or protected direct (since C++17)non-static data members. no user-declared constructors.
Indeed,
Variadic template is a template, which can take an arbitrary number of template arguments of any type. Both the classes & functions can be variadic.
In respect to this,
The name derives from variadic functions in C (and C++) such as printf which take a variable number of arguments. Unlike variadic function which iterate over their arguments at runtime (and perform type erasure and are generally unsafe), variadic templates collect template parameters in parameter packs which are expanded at compile time.