Exception Specifications

Exception specifications in C++ are a way to specify which exceptions a function can throw. They provide a contract between the function and its caller, indicating the types of exceptions that may be thrown by the function.

In modern C++, there are two types of exception specifications:

1. noexcept specification: It indicates that the function does not throw any exceptions. If an exception is thrown from a noexcept function, it will result in a call to std::terminate.
2. Dynamic exception specification (deprecated): It specifies the types of exceptions that a function can throw using the throw keyword followed by a list of exception types. However, dynamic exception specifications are deprecated since C++11 and should be avoided.

Here's an example of using the noexcept specification:

1void foo() noexcept {
2  // Function body
3}

In this case, the foo function is marked as noexcept, indicating that it does not throw any exceptions.

When should you use exception specifications?

Use noexcept for functions that are guaranteed not to throw

• If a function is designed not to throw any exceptions, you can mark it as noexcept to provide a strong guarantee to the caller.
• This can help the compiler optimize the code and improve performance, as it knows that no exceptions will be thrown.

Use noexcept for move constructors and move assignment operators

• Move operations are typically expected to be noexcept to enable efficient move semantics and optimization.
• If a move constructor or move assignment operator throws an exception, it can lead to unexpected behavior and resource leaks.

Avoid using dynamic exception specifications

• Dynamic exception specifications using the throw keyword are deprecated and should be avoided in modern C++.
• They have several drawbacks, such as runtime overhead, limited compiler optimizations, and potential inconsistencies between the specification and the actual exceptions thrown.

Here's an example of a move constructor marked as noexcept:

1class MyClass {
2public:
3  MyClass(MyClass&& other) noexcept {
4    // Move constructor implementation
5  }
6  // ...
7};

In this case, the move constructor of MyClass is marked as noexcept, indicating that it does not throw any exceptions during the move operation.

It's important to note that exception specifications are part of the function's interface and should be used judiciously. They should be applied when there is a clear and well-defined contract regarding the exception behavior of a function.

In general, it's recommended to use noexcept for functions that are guaranteed not to throw and for move operations, while avoiding the use of dynamic exception specifications. The decision to use exception specifications should be based on the specific requirements and design of your code.