Re: Readline using foreach and while

Ben Morrow wrote:
Quoth "szr" <szrRE@xxxxxxxxxxxxxxx>:

Actually the behaviors of "for (@ary)" and "for (@ary, ())" do seem
consistant if you really think about it. The resulting list is what
it iterates over (from the first element, to what ever *count* is...
in the former case *count* come fro mthe array, and since the
condition is checked at the start of each iteration, if the array is
added to, the count is incremented.

In the latter case, a new list is created from contents of @ary + an
empty list, which gives you a new list, which contains the values of
@ary, but is a new seperate list, and thus is not effected by
changes to @ary because it has it's own copy of @ary's values.

OK, now explain to me why

my @ary = qw/a b c/;
print map { /c/ and push @ary, 'd'; $_ } @ary;

*doesn't* work like that :).

Actually it does. The difference is, map doesn't recheck the count every
time around like for/foreach do. If you print the contents of @ary after
the line with the map statement, it does indeed contain 'd' at the end.
This behavior seems to correct, as one would likely expect that the list
map returns when it is finished to be the same length as the one
/passed/ into map at the start. If you pass a 3 element list, you should
get back a 3 element list, should you not? Or do you consider this to be
a bug?

However, consider:

my @ary = qw/a b c/;
print map { /c/ and $_ = 'd'; $_ } @ary;


__OUTPUT__
abd

$_ is aliased to the current array element just like in for. Again, the
only difference I see if that map doesn't recheck the count of the
passed list for each iteration. Well, that and map returns a list :-)

To me, this behavior is part of what separates map from for/foreach.

--
szr


.

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