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C++ Templates
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C++ Templates

C++ Templates

1. Creating First Template
Introduction to TemplatesCreating Your First TemplateUsing Template FunctionMultiple TypenamesTypename Naming Conventions
2. Templates Usage
The Purpose of TemplatesPassing Multiple Arguments with Different Types
3. Template Specialization
Understanding Type ConstraintsTemplate SpecializationVariadic Templates
4. Class
Class Template
5. Template Metaprogramming
Understanding constexpr Functions and VariablesIntroduction to constexpr with TemplatesTemplate aliases and variadic templatesCompile-Time Computation with Templates

Compile-Time Computation with Templates

Templates are not just a tool for creating generic algorithms and data structures; they also unlock the power of compile-time computation. This technique allows for the execution of certain programs during the compilation phase, leading to optimized and faster executable code.

Understanding Factorial Calculation

Factorial, denoted as "n!", is the product of a positive integer and all the positive integers below it. For instance, 4! = 4 * 3 * 2 * 1 = 24. Traditionally, the factorial function is implemented recursively, with a runtime computation for any given input n. This approach, while straightforward, doesn't leverage the knowledge of n at compile time, leading to unnecessary runtime calculations.

Traditional Implementation

cpp

main

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#include <iostream>

int factorial(int n) {
  if (n == 0)
    return 1;
  else
    return n * factorial(n - 1);
}

int main()
{
    std::cout << factorial(4); // Computes 24 at runtime
}

This method computes factorial(4) at runtime, which is not efficient when the value of n is known at compile time.

Compile-Time Computation with Templates

To harness the full potential of compile-time computation, we use template metaprogramming. This approach computes the factorial at compile time, thus eliminating runtime overhead and shrinking the code footprint.

cpp

main

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#include <iostream>

template <int N>
struct Factorial {
  static const int value = N * Factorial<N - 1>::value;
};

template <>
struct Factorial<0> { // Base case specialization
  static const int value = 1;
};

int main()
{
	std::cout << Factorial<4>::value; // 24, computed at compile time
}

In this template-based meta-program, Factorial::value recursively computes the factorial of N, with a specialization for Factorial<0> to handle the base case. This results in the factorial of 4 being calculated during the compilation phase, significantly speeding up execution time as the computation is moved from runtime to compile time.

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Seção 5. Capítulo 4
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