Re: Will "$_[0]=shift" always resolve shift first?

As you can see from the listing in perlop, the assignment operator ("=") has right associativity, which means that the right side is evaluated before the left side.

Incidentally, this is the very reason that the following common idiom works as you expect:

$x = $y = 42;
[download]

Had "=" its left side evaluated first, the 42 would not make it into the $y variable, which would lead to code breakage all over the planet ;)

Update: Hm, scratch that, I think I confused a few terms. The associativity tells us how the statement gets parsed, not how it gets executed.

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Re^2: Will "$_[0]=shift" always resolve shift first? by ikegami (Patriarch) on Sep 08, 2008 at 22:00 UTC
Associativity controls the order in which operators are evaluated in a chain of operators of the same precedence. If operand evaluation order was tied to operator precedence and associativity, `bar()` would be evaluated before `foo()` in `foo() + bar() * baz()` [download] (It's not.)	[reply] [d/l] [select]
Re^2: Will "$_[0]=shift" always resolve shift first? by GrandFather (Saint) on Sep 08, 2008 at 23:55 UTC
So what would you expect the following to print? `use strict; my @array = (0, 0, 0); my $x = 0; $array[++$x] = $x++; print "@array\n"; $x = 0; $array[++$x] = $x; print "@array\n"; $x = 0; $array[++$x] = ++$x; print "@array\n";` [download] <Reveal this spoiler or all in this thread> Perl reduces RSI - it saves typing	[reply] [d/l] [select]
Re^3: Will "$_[0]=shift" always resolve shift first? by ikegami (Patriarch) on Sep 09, 2008 at 00:16 UTC
What is your point? If your point was to contradict betterworld, it doesn't. While it may not appear to be the case, the RHS of the assignment is evaluated before the LHS in every instance. If your point is that it can get very complex very fast, I agree.	[reply]
Re^4: Will "$_[0]=shift" always resolve shift first? by GrandFather (Saint) on Sep 09, 2008 at 01:14 UTC
In the last case (`$array[++$x] = ++$x;`) both $x pre-increments are evaluated before the content of $x is returned as the value for the RHS (2 is assigned) so at least part of the LHS calculation is performed before the RHS is fully evaluated. Perl reduces RSI - it saves typing	[reply] [d/l]
Re^5: Will "$_[0]=shift" always resolve shift first? by ikegami (Patriarch) on Sep 09, 2008 at 01:57 UTC
Re^6: Will "$_[0]=shift" always resolve shift first? by GrandFather (Saint) on Sep 09, 2008 at 03:16 UTC


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