Re^3: Summing Up Array Elements By Group

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Re^4: Summing Up Array Elements By Group by gwadej (Chaplain) on Jan 21, 2009 at 18:55 UTC
`$b++` makes a copy so that it can return the previous value. `++$b` does not need to. I have run into this issue before in C++, but it was normally not a problem for integers. Scalars on the other hand are a different beast. G. Wade	[reply] [d/l] [select]
Re^5: Summing Up Array Elements By Group by ikegami (Patriarch) on Jan 21, 2009 at 19:39 UTC
it was normally not a problem for integers. I find it odd that it would matter at all for ints. `++a --- inc a mov a, reg a++ --- mov a, reg inc a` [download]	[reply] [d/l]
Re^6: Summing Up Array Elements By Group by gwadej (Chaplain) on Jan 21, 2009 at 20:32 UTC
It doesn't matter for `int`s. But, for various kinds of iterators and other classes supporting `++` it can. (I guess I didn't make that clear.) That's why the suggested practice in C++ lately has been to use `++a` unless you actually need the previous value. That way when you replace that index with an iterator things don't get any slower. G. Wade	[reply] [d/l] [select]
Re^4: Summing Up Array Elements By Group by ikegami (Patriarch) on Jan 21, 2009 at 18:57 UTC
`$b++` needs to create a new anonymous scalar because the result is different than the $b. `++$b` just returns a pointer to `$b`. `$ perl -le'my $b = 4; $r = \( $b++ ); $$r = 20; print $b' 5 $ perl -le'my $b = 4; $r = \( ++$b ); $$r = 20; print $b' 20` [download]	[reply] [d/l] [select]
Re^5: Summing Up Array Elements By Group by hbm (Hermit) on Jan 21, 2009 at 19:06 UTC
Nice! One point for your original and another for gwadej's explanation.	[reply]


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