Variable Templates

Variable Templates vs Constexpr Variables

How do variable templates differ from constexpr variables?

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Variable templates and constexpr variables are related but have some key differences:

  • Variable templates allow you to define a variable that can be instantiated with different types. They provide a way to create variables with parameterized types, similar to how function templates allow functions to work with different types. Variable templates are defined using the¬†template¬†keyword followed by template parameters.
  • Constexpr variables, on the other hand, are variables that are evaluated at compile-time and have a constant value. They are defined using the¬†constexpr¬†keyword and must be initialized with a constant expression. Constexpr variables can be of any type, but their value must be known at compile-time.

Here's an example to illustrate the difference:

// Variable template
template <typename T>
constexpr T pi = T(3.14159265358979323846);

// Constexpr variable
constexpr double e = 2.71828182845904523536;

int main() {
  // Instantiating the variable template with double
  double pi_double = pi<double>;
  
  // Instantiating the variable template with float
  float pi_float = pi<float>;

  // Using the constexpr variable
  double result = e * 2;
}

In this example, pi is a variable template that can be instantiated with different types, such as double or float. Each instantiation creates a separate variable with the specified type and initializes it with the provided value.

On the other hand, e is a constexpr variable of type double. Its value is fixed and known at compile-time. The key difference is that variable templates allow for type parameterization, while constexpr variables have a fixed type and value determined at compile-time.

Both variable templates and constexpr variables are useful for creating compile-time constants and performing compile-time computations, but variable templates offer additional flexibility in terms of type parameterization.

This Question is from the Lesson:

Variable Templates

An introduction to variable templates, allowing us to create variables at compile time.

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This Question is from the Lesson:

Variable Templates

An introduction to variable templates, allowing us to create variables at compile time.

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