Re: Variant of map for special-casing the last item

I probably would have this in 5.8:

$ cat sentinel_58.pl
#!perl

use strict;
use warnings;

my @in = qw{start middle end};
my $i = 0;
print map {
    join($_, ($i++ == $#in ? q{<li class="last">} : q{<li>}), q{</li>}
+);
} @in;

$ sentinel_58.pl
<li>start</li><li>middle</li><li class="last">end</li>
[download]

And here's much the same offering for newer Perl versions:

$ cat sentinel_512.pl
#!perl

use 5.12.0;
use warnings;

my @in = qw{start middle end};
say map {
    state $i = 0;
    join($_, ($i++ == $#in ? q{<li class="last">} : q{<li>}), q{</li>}
+);
} @in;

$ sentinel_512.pl
<li>start</li><li>middle</li><li class="last">end</li>
[download]

-- Ken

Comment on Re: Variant of map for special-casing the last item Select or Download Code

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Re^2: Variant of map for special-casing the last item by jdporter (Paladin) on Oct 26, 2010 at 13:44 UTC
I definitely like the use of a state variable way more than the 5.8 approach. But what I still don't like about this and similar solutions is that they introduce a dependency inside the code block on the value of `$#in`. What if the input list isn't in an array variable? That's right — you can store it in a temporary. Well, that's what my solution does for you, keeping that mess out of your code. What is the sound of Windows? Is it not the sound of a wall upon which people have smashed their heads... all the way through?	[reply] [d/l]
Re^3: Variant of map for special-casing the last item by kcott (Archbishop) on Oct 26, 2010 at 18:34 UTC
I wrote the 5.12 code first then, realising many people haven't moved past 5.8 yet, wrote the second version - I probably should have posted them in that order. Being able to confine the scope of a variable to a `map` (or similar) block via `state` in this way is a nice feature. I agree, this solution is not directly applicable to situations like `map {...} qw{...}`. -- Ken	[reply] [d/l] [select]