Using static_assert in Template Code

The lesson shows an example of using static_assert() with std::is_floating_point to validate template parameters. What are some other common type traits I can use for template validation?

static_assert() is extremely useful in template code for validating template parameters at compile-time. It allows you to provide clearer error messages and avoid instantiating invalid template specializations.

Here are some common type traits from the <type_traits> header that are useful for template validation:

Example 1: std::is_integral and std::is_floating_point:

template <typename T>
T sum(T a, T b) {
  static_assert(std::is_integral<T>::value ||
                std::is_floating_point<T>::value,
                "sum() requires numeric types");
  return a + b;
}

Example 2: std::is_base_of:

template <typename T>
class Derived : public T {
  static_assert(std::is_base_of<Base, T>::value,
                "T must be derived from Base");
  // ...
};

Example 3: std::is_same:

template <typename T, typename U>
void assert_same() {
  static_assert(std::is_same<T, U>::value,
                "Types must be the same");
}

Example 4: std::is_pointer and std::is_reference:

template <typename T>
void process(T t) {
  static_assert(!std::is_pointer<T>::value,
                "Pointers are not allowed");
  static_assert(!std::is_reference<T>::value,
                "References are not allowed");
// ...
}

Example 5: std::is_constructible:

template <typename T, typename... Args>
void construct(Args&&... args) {
  static_assert(std::is_constructible<T, Args...>::value,
                "T must be constructible from Args");
  T obj(std::forward<Args>(args)...);
// ...
}

These are just a few examples. The <type_traits> library provides many more type traits for checking properties like const-qualification, volatility, trivial constructibility, default constructibility, and more.

In C++17 and later, you can use the _v suffixed versions of the type traits for a more concise syntax:

template <typename T>
void foo(T t) {
  static_assert(std::is_integral_v<T>,
                "foo() requires an integral type");
  // ...
}

Using type traits with static_assert in your template code can lead to more expressive and self-documenting interfaces, as well as clearer error messages for users of your templates.

Errors and Assertions

Learn how we can ensure that our application is in a valid state using compile-time and run-time assertions.

Questions & Answers

Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

Using Assert in Release Builds
The lesson mentions that assert() calls are sometimes stripped out in release builds for performance. What if I want to keep some critical assertions enabled in release builds?
Using static_assert with Non-constexpr Expressions
Can static_assert() be used with expressions that are not known at compile-time, such as values read from a file or user input?
Avoiding Side Effects in Assertions
Is it okay to use assert() with expressions that have side effects, like assert(++x > 0)? Or should assertions be side-effect free?
Assertions vs Exceptions
When should I use assertions vs throwing exceptions? They seem to serve similar purposes.
Defensive Programming with Assertions
How can I use assertions to practice "defensive programming" and make my code more robust?
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