sk::error

sk:error is a simple container class for passing exceptions by value. Its primary purpose is to allow exceptions to be returned by value in code paths where exceptions are undesirable. This allows exception-free code to re-use existing exception hierarchies to describe error conditions.

Note that sk:error itself is not guaranteed to be exception free (for example, it can throw std::bad_alloc during construction) but it does not throw exceptions during normal operation.

Interface reference

The sk:error object is copyable and movable, and can be constructed from any object that derives from std::exception.

• auto what() const -> char const *: Return the stored exception's what().
• operator bool() const: Return true if the error object is empty (i.e., indicates success and does not contain an exception object), or false if an error condition is present.
• auto is<T>() const -> bool: Return true if the error is non-empty and contains an exception type which is or derives from T.
• auto get<T>() const -> T const *: If is<T>(), return the value of the stored exception.

Installation

sk::error is a single-header library, so you can simply drop the header file into your source tree. If your project uses CMake, you can add the entire project as a subdirectory (e.g., with Git submodules) and link with the sk-error library.

Sample usage

sk::error print_non_empty_string(char const *str) {
	if (!*str)
		return std::domain_error("string cannot be empty")
	std::cout << str << '\n';
	return sk::error();
}

int main(int argc, char **argv) {
	auto err = print_non_empty_string(argv[1]);
	if (!err)
		std::cerr << "could not print the string: " << err.what() << '\n';
	return 0;
}

Errors can be tested for type (requires RTTI):

	auto err = f();
	if (err.is<std::domain_error>())
		std::cout << "domain error\n";

The base exception type can be retrieved (requires RTTI):

	auto err = f();
	std::domain_error *domerr = err.get<std::domain_error>();

sk::error works well with "expected" / "outcome" interfaces:

expected<int, sk::error> unhelpful_abs(int i) {
	if (i < 0)
		return -i;

	return make_unexpected(std::domain_error("integer must be negative"));
}