Programming Perl

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3.2.71 goto

goto LABEL
goto EXPR
goto &NAME

goto LABEL finds the statement labeled with LABEL and resumes execution there. It may not be used to go into any construct that requires initialization, such as a subroutine or a foreach loop. It also can't be used to go into a construct that is optimized away. It can be used to go almost anywhere else within the dynamic scope,[4] including out of subroutines, but for that purpose it's usually better to use some other construct such as last or die. The author of Perl has never felt the need to use this form of goto (in Perl, that is - C is another matter).

[4] This means that if it doesn't find the label in the current routine, it looks back through the routines that called the current routine for the label, thus making it nearly impossible to maintain your program.

Going to even greater heights of orthogonality (and depths of idiocy), Perl allows goto EXPR, which expects EXPR to evaluate to a label name, whose scope is guaranteed to be unresolvable until run-time since the label is unknown when the statement is compiled. This allows for computed gotos per FORTRAN, but isn't necessarily recommended[5] if you're optimizing for maintainability:

[5] Understatement is reputed to be funny, so we thought we'd try one here.

goto +("FOO", "BAR", "GLARCH")[$i];

goto &NAME is highly magical, substituting a call to the named subroutine for the currently running subroutine. This is used by AUTOLOAD subroutines that wish to load another subroutine and then pretend that this subroutine - and not the original one - had been called in the first place (except that any modifications to @_ in the original subroutine are propagated to the replacement subroutine). After the goto, not even caller will be able to tell that the original routine was called first.

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