{"id":4554,"date":"2022-11-08T11:23:09","date_gmt":"2022-11-08T09:23:09","guid":{"rendered":"https:\/\/mariusbancila.ro\/blog\/?p=4554"},"modified":"2022-11-08T11:23:12","modified_gmt":"2022-11-08T09:23:12","slug":"three-new-utility-functions-in-cpp23","status":"publish","type":"post","link":"https:\/\/mariusbancila.ro\/blog\/2022\/11\/08\/three-new-utility-functions-in-cpp23\/","title":{"rendered":"Three new utility functions in C++23"},"content":{"rendered":"\n

Some time ago I wrote a blog post called Three C++23 features for common use<\/a>. In this article, I want to continue on that idea and discuss three new utility functions that were added to C++23.<\/p>\n\n\n\n\n\n\n\n

std::unreachable<\/h3>\n\n\n\n

This new function is available in the <utility><\/code> header. It’s intended to be used when you know you have an execution path in your code that cannot be reached but the compiler cannot figure that out. Informing the compiler could help to optimize impossible code branches.<\/p>\n\n\n\n

A typical use case for this function are switch statements on a variable that can take only a limited set of values from its domain. For instance, an integer that can only be between 0 – 9. Here is a simple example with a switch that checks a char<\/code> value and executes operations. Only a limited number of commands are supported but the argument is checked before invoking the function so it shouldn’t be possible to receive other values than already handled in the switch.<\/p>\n\n\n\n

void execute_command(char ch)\n{\n   switch (ch)\n   {\n   case 'a':\n      \/* add *\/ break;\n   case 'd':\n      \/* delete *\/ break;\n   default:\n      std::unreachable();\n   }\n}\n\nbool is_valid(char ch)\n{\n   return ch == 'a' || ch == 'd';\n}\n\nint main()\n{\n   char ch = 0;\n   while (!is_valid(ch))\n      std::cin >> ch;\n   execute_command(ch);\n}<\/pre>\n\n\n\n
It could be argued though that it might be safer to handle the default case in some way to ensure safe failure rather than assume that a variable\/argument would always take a limited number of values. This depends on the particularities of your code.<\/p>\n\n\n\n
It should be noted that std::unreachable<\/code> invokes undefined behavior. <\/p>\n\n\n\n
Learn more<\/strong><\/p>\n\n\n\n