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Please explain me the rules for template specialization selection. I have an example:
template<typename T1, typename T2 = int>
struct S : false_type{};
template<typename T>
struct S<T, float> : true_type{};
cout << boolalpha << S<float>::value;
Why the output is false? And in general, what happens with default template parameter typename T2 = int in specialized classes? Does it introduces some influence?
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This is called template specialization. Template allows us to define generic classes and generic functions and thus provide support for generic programming. Generic programming is an approach where generic data types are used as parameters in algorithms so that they work for variety of suitable data types.
The act of creating a new definition of a function, class, or member of a class from a template declaration and one or more template arguments is called template instantiation. The definition created from a template instantiation is called a specialization.
What Does Template Mean? A template is a C++ programming feature that permits function and class operations with generic types, which allows functionality with different data types without rewriting entire code blocks for each type.
A class template can be declared without being defined by using an elaborated type specifier. For example: template<class L, class T> class Key; This reserves the name as a class template name. All template declarations for a class template must have the same types and number of template arguments.
Choosing a template specialization happens in five steps:
<T1, T2 = int> S)T1 <- float)T2 <- int)<float, int> does not match <T, float>, so ignore the specialization; only possibility left is primary template)
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