Rule A15-1-3 (advisory, implementation, automated)

All thrown exceptions should be unique.

Rationale

Defining unique exceptions in the project significantly simplifies debug process. An exception is considered to be unique if at least one of the following conditions is fulfilled: The type of the exception does not occur in any other place in the project The error message (i.e. message itself, error code, etc.) of the exception does not occur in any other place in the project

Example

//% $Id: A15-1-3.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <iostream>
#include <sstream>
#include <stdexcept>
#include <string>
static std::string ComposeMessage(const char* file,

const char* func,
std::int32_t line,
const std::string& message) noexcept

{
std::stringstream s;
s << "(" << file << ", " << func << ":" << line << "): " << message;

return s.str();
}
void F1()
{
// ...
throw std::logic_error("Error");
}
void F2()
{
// ...
throw std::logic_error("Error"); // Non-compliant - both exception type and
// error message are not unique
}
void F3()
{
// ...
throw std::invalid_argument(
"Error"); // Compliant - exception type is unique
}
void F4() noexcept(false)
{
// ...
throw std::logic_error("f3(): preconditions were not met"); // Compliant // error
// message is
// unique

}
void F5() noexcept(false)
{
// ...
throw std::logic_error(ComposeMessage(
__FILE__,
__func__,
__LINE__,
"postconditions were not met")); // Compliant - error message is unique
}
void F6() noexcept
{
try
{
F1();
F2();
F3();
}

catch (std::invalid_argument& e)
{
std::cout << e.what() << ’\n’; // Only f3() throws this type of
// exception, it is easy to deduce which
// function threw

}

catch (std::logic_error& e)
{
std::cout << e.what() << ’\n’; // f1() and f2() throw exactly the same
// exceptions, unable to deduce which
// function threw
}

try
{
F4();
F5();
}

catch (std::logic_error& e)
{
std::cout << e.what() << ’\n’; // Debugging process simplified, because
// of unique error message it is known
// which function threw
}
}

See also

Effective Java 2nd Edition [15]: Item 63: Include failure-capture information in detail messages