Rite, Block locals and Autovivification

[John Carter]

Perl has what may be an evil solution block locals.

Certainly maximal surprise but Does What I Mean....

What does the bit of Perl
$a{foo}++
do?

Well, you clearly are referring to a hash, so it makes one.

Since foo doesn't have a sigil, it takes it as a string...
$a{'foo'}++

Since the element doesn't exists yet, and we're adding one to it, it
"autovivifies" or "magically grants life" to it. Namely 0. Perl chose 0
since that is "What I Mean" when I add one to and uninitialised something.

Now to Ruby...

def each_anime(io)
io.each do |line|
next unless line =~ /evangelion|omg|spirited/
l = line.length # l is just local to block
map[$1] = line # Autovivifies map as Hash
count += 1 # Auto vivifies as 0 on first pass, an gives it scope
# beyond block.
weight *= 0.2 # Autovivifies as 1

yield line
end
# l is out of scope here
[count,weight,map] # Visible at function scope as autovivified.
end



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[gabriele renzi]

il Tue, 2 Dec 2003 06:35:18 +0900, John Carter

Perl has what may be an evil solution block locals.

Certainly maximal surprise but Does What I Mean....

Just my personal feeling.. but I'd hope to avoid stuff like this in
ruby.
It is fun, powerful and absolutely intrinsic and hard to understand.
[1]

I'm not saying this is really bad, just I'd prefer this does'nt
appear.
I strongly believe 'explicit is better than implicit'.
plus, a single line:
map, count,weight={},0,1
would make this work. Not so much a big cost for me


[1]
If you're going to say 'no, let me explain, this is really clean and
intuitive' please consider that i really think this is hard to grasp