Variable Templates with Custom Types

Yes, you can use variable templates with user-defined types. The type used in a variable template can be any valid C++ type, including user-defined types such as classes or structs. However, there are a few requirements for using user-defined types with variable templates:

• The user-defined type must have a constexpr constructor that can accept the arguments passed to the variable template.
• The user-defined type must be default-constructible if no arguments are provided to the variable template.

Here's an example of using a variable template with a user-defined type:

1struct MyType {
2  constexpr MyType(int value) : value(value) {}
3  int value;
4};
5
6template <typename T>
7constexpr T myVariable = T(42);
8
9int main() {
10  // v.value will be 42
11  MyType v = myVariable<MyType>;
12}

In this example, MyType is a user-defined type with a constexpr constructor that accepts an int value. The variable template myVariable is defined with a type parameter T and initializes the variable with T(42). When myVariable is instantiated with MyType, it creates an instance of MyType with the value 42.