I concur with everything
tilly said above. To summarize, a
goto is not considered harmful when you're:
- replacing the current subroutine via a goto &othersub (rare),
- autogenerating code that will never be seen or maintained directly (rarer),
- implementing a flow-of-control that Perl doesn't support natively (rarest).
For me, the key point in tilly's reply is that virtually all other "legitimate" uses of a goto in other languages are made redundant in Perl by the availability of named loops.
Whereas in C/C++ you might reasonably have to write:
for (i=1; i<10; i++) {
for (j=1; j<10; j++) {
for (k=1; k<10; k++) {
/* Process data[i][j][k] here */
if (data[i][j][k] < threshold) goto EOLOOPS;
}
}
}
EOLOOPS:
Perl has a much cleaner way to escape from a deep nesting:
LOOPS: for $i (1..10) {
for $j (1..10) {
for $k (1..10) {
# Process $data[$i][$j][$k] here
last LOOPS if $data[$i][$j][$k] < $threshold;
}
}
}
Long ago, before I discovered the Way of the Camel, I used to rely on a couple of moderately evil preprocessor commands to give myself named loops in C/C++ too:
#define named(name) goto name; name##_break: if (0) name:
#define break(name) goto name##_break;
/* Which then allows you to write... */
named (LOOPS) for (i=1; i<10; i++) {
for (j=1; j<10; j++) {
for (j=1; j<10; j++) {
/* Process data[i][j][k] here */
if (data[i][j][k] < threshold) break(LOOPS);
}
}
}
Exploring how those
#defines work -- and why they don't interfere with the semantics of normal (unnamed)
break statements -- is left as an exercise for those of you who still follow the Dark Path.
;-)
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.