goto transfers execution to a specified point in the program. Unlike a function call, execution does not return togoto.
Thegoto LABEL form finds the statement labeled with LABEL and resumes execution there. It can't be used to get out of a block or subroutine given tosort. It can be used to go almost anywhere else within the dynamic scope, including out of subroutines, but it's usually better to use some other construct such aslast ordie. The author of Perl has never felt the need to use this form ofgoto (in Perl, that is; C is another matter). (The difference is that C does not offer named loops combined with loop control. Perl does, and this replaces most structured uses ofgoto in other languages.)
Thegoto EXPR form expects to evaluateEXPR to a code reference or a label name. If it evaluates to a code reference, it will be handled likegoto &NAME, below. This is especially useful for implementing tail recursion viagoto __SUB__.
If the expression evaluates to a label name, its scope will be resolved dynamically. This allows for computedgotos per FORTRAN, but isn't necessarily recommended if you're optimizing for maintainability:
goto ("FOO", "BAR", "GLARCH")[$i];As shown in this example,goto EXPR is exempt from the "looks like a function" rule. A pair of parentheses following it does not (necessarily) delimit its argument.goto("NE")."XT" is equivalent togoto NEXT. Also, unlike most named operators, this has the same precedence as assignment.
Use ofgoto LABEL orgoto EXPR to jump into a construct is deprecated and will issue a warning; it will become a fatal error in Perl 5.42. While still available, it may not be used to go into any construct that requires initialization, such as a subroutine, aforeach loop, or agiven block. In general, it may not be used to jump into the parameter of a binary or list operator, but it may be used to jump into thefirst parameter of a binary operator. (The= assignment operator's "first" operand is its right-hand operand.) It also can't be used to go into a construct that is optimized away.
Thegoto &NAME form is quite different from the other forms ofgoto. In fact, it isn't a goto in the normal sense at all, and doesn't have the stigma associated with other gotos. Instead, it exits the current subroutine (losing any changes set bylocal) and immediately calls in its place the named subroutine using the current value of@_. This is used byAUTOLOAD subroutines that wish to load another subroutine and then pretend that the other subroutine had been called in the first place (except that any modifications to@_ in the current subroutine are propagated to the other subroutine.) After thegoto, not evencaller will be able to tell that this routine was called first.
NAME needn't be the name of a subroutine; it can be a scalar variable containing a code reference or a block that evaluates to a code reference.
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