Do Or Die

A programming idiom, common in PerlLanguage, CeeLanguage, and other Unix scripting languages (BourneShell, CeeShell) used for error handling.

The idiom is essentially to write code such as the following:

 take_some_action() || handle_the_error();

In PerlLanguage, the way errors are often handled is to throw an exception using Perl's die command, hence DoOrDie. In PHP, the code looks like this:

 DoSomething?() or die("Something failed");

This relies on two things:

• In the languages in question, it is common for a function to return a boolean true value on success, false on failure. (Unix convention is for spawned processes to do the opposite; one uses exit(0) to signify success and exit(1) to signify failure. Unix shells therefore invert the return value to get the true/false value for the shell to evaluate).

• The boolean OR operator has short circuit semantics.

If the operation succeeds (returns true), then the result of the OR is true and the handle_the_error() code is not executed. If the operation fails, then the handle_the_error() code is executed. Note that usually with DoOrDie the result of the boolean OR operator is not of interest; only its side-effects.

One can do similar stuff with boolean AND to chain operations, ensuring that subsequent operations are only run if their predecessor succeeded.

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I'm not normally against exceptions, but in Perl's case the primitive implementation really kills the utility. Making a %SIG{__DIE__} handler useful can be quite a pain. -PA

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Why can't you use eval {}?

Perl 5's eval {...};if ($@) {...} is other languages try's equivalent

- Pawel Murias

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Topic not to be confused with LimpVersusDie.

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CategoryIdiom, CategoryException