Re^2: How to return a two dimensional array from a function in Perl?

and and or are designed to be used to join statements. Use && and || inside of expressions.

Huh? What practical difference is there between this:

if (($graph[$i][$j] == 0) and ($i != $j))
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and this:

if (($graph[$i][$j] == 0) && ($i != $j))
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apart from the fact the former is more English-like? Isn't each condition around the conjunction a kind of statement? (What exactly is the difference between a "statement" and an "expression"? -- actually, I'm not sure I want to get into that...)

Comment on Re^2: How to return a two dimensional array from a function in Perl? Select or Download Code

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Re^3: How to return a two dimensional array from a function in Perl? by ikegami (Patriarch) on Nov 03, 2008 at 04:44 UTC
What practical difference is there between this: One practice is more likely to eventually burn you than the other. What exactly is the difference between a "statement" and an "expression"? I suppose it'd be safer to look at whether the program's flow is being controlled or not. `or next`, `or return`, `or die`, etc.	[reply] [d/l] [select]
Re^4: How to return a two dimensional array from a function in Perl? by graff (Chancellor) on Nov 03, 2008 at 19:31 UTC
One practice is more likely to eventually burn you than the other. Please correct me if I'm wrong: The important point about choosing between "`and/or`" vs. "`&&/\|\|`" involves their differences in precedence relative to other operators (especially the "comma operator"); the classic example (often seen in SoPW questions) being: `open $fh, "<", $filename \|\| die "oops!"; # should use "or" here # (or else put parens around the args for the " +open()" call)` [download] But the "burn" only happens when you use `&&/\|\|` in a context where `and/or` would be needed to do the right thing. In contrast, I can't think of any context appropriate for `&&/\|\|` such that `and/or` wouldn't serve equally well. If you can find a context where `&&/\|\|` produce an intended result and replacing them with `and/or` produces a different (incorrect) result, that would be remarkably informative (and surprising, I think). NB: No fair making up obfu examples that depend on l-to-r vs. r-to-l differences -- people who get into that kind of trouble need other kinds of help and advice. I'm guessing that BrowserUK has a similar view, and the reason we're both giving you grief about this is that you seem to be suggesting there are situations where using `and/or` should be disfavored or unadvisable, whereas B and I would rather say that the better advice is "when in doubt, use `and/or`" (which is what the OP seemed to be doing in the first place).	[reply] [d/l] [select]
Re^5: How to return a two dimensional array from a function in Perl? by ikegami (Patriarch) on Nov 03, 2008 at 21:43 UTC
If you can find a context where `&&/\|\|` produce an intended result and replacing them with `and/or` produces a different (incorrect) result, that would be remarkably informative Easy. Consider rewriting `if ($a == 1 or $b == 2) { ... }` [download] so that a variable is used to hold the condition. `my $cond = $a == 1 or $b == 2; XXX if ($cond) { ... }` [download] Why write the same expression two different ways depending on context?	[reply] [d/l] [select]