Pick on a common example of code that can easily be improved using idiomatic constructs. Something like changing C-style for(;;)'s to foreach(@array) or map{..}@array. Make the first change manually explaining the reasons and benefits,

I realize you probably just quickly chose a this construct as an example. But your choice is unfortunate.

Changing C-style loops to foreach loops is not as trivial as you would have it appear. The presentation would be impressive, but misleading.

I might point out the advantages of foreach loops. And how the C-style loop is more cumbersome but more adaptable. These folk are probably very comfortable with this C phrasing. Saying this is how to improve the code is unnecessary optimization and quibbling over style at the risk of breakage.

I like presentations that include workload and mental state, to wit:

"It took me two hours to decipher this code."
"Thirty minutes to get this rewrite, that has these problems. Notice how I used ..."
"A hour of exploratory testing and minor tweaks. At this point I felt like I had a good understanding of ..."

To the original post:

If these are not fairly simple scripts and requirements are vague I'd first want my crew to instrument the old stuff to tee off both I and O on demand. Assuming this is reasonable.

I cannot imagine the function-free java code these people are writing.

But your choice is unfortunate.

Interesting comment. Id be interested in hearing more about why you think this was an unfortunate choice.

And how the C-style loop is more cumbersome but more adaptable.

A C-Style for loop is always functionally and internally equivelent to a suitably constructed while loop. The primary differences being that many programmers from a C tradition find the for(;;) syntax more readable, while the rest of us find the while syntax more readble and maintainable. I am in the latter group. :-) Nine time out of ten (more really) when I see someone use a C-Style for loop they are not exploiting the equivelence to a while , but rather using a slightly less readble, more error prone and less efficient form of a for (LIST) loop. I avoid the term foreach because foreach is a synonym to for in perl, they are identical.

E:\Smoke\source>perl -e "foreach (my $i=0;$i<10;$i++) { print $i,$/}"
E:\Smoke\source>perl -e "for     (my $i=0;$i<10;$i++) { print $i,$/}"
[download]

Insofar that the majority of its use is to simulate for ($m..$n) where $m<$n I think advising people to convert to the more legible and less error prone form is probably a good idea. And I also think that its a good idea to use while () {} continue {} instead of for(;;) if only because it tends to be easier to read. Having said that in the time ive been using perl I think ive needed the construct a mere handful of times.

Ultimately id argue that for(;;) is a construct mostly provided to reduce the pain for C junkies, and that in the long term better constructs that are more intuitive and less error prone are available and so should be encouraged.

--- demerphq
my friends call me, usually because I'm late....

Having said that in the time ive been using perl I think ive needed the construct a mere handful of times.

To reinforce the point.. I've literally never used it. There was not a single instance I wasn't equally or better served with the other constructs.

And to be honest, considering the number of cases I advised people not to use for(;;) for whatever they were using it for, and the number of times I restructured loops in others' code to not use it, if it was to disappear from the language I wouldn't shed a tear. Actually, scratch that, I'd be cheering.

Makeshifts last the longest.

There is not much more. The context was about changing  for(;;) to  for(@array) or to  map {} @array and doing it with an editor macro to the worst work of a weak group of perlers. In a training presentation to that group.

My points were:

• This, in its presentation, would trivialize the issues.
• The  for(;;) and  for(LIST) constructs are very different.
• This a rather small issue, surely there are more important problems in the above situation.

Your comparison of the  for(;;) and  while loops is a different issue. For the simple cases I prefer a  for( $i=1; $i < 10_000_000; $i++) as all the loop's controls are there upfront. This assumes good practice, i.e. you don't fiddle with  $i while looping. If you mess with  $i then you should use a  while loop.

You say:

Usually when someone uses a C-Style for loop they are not exploiting the equivalence to a while , but rather using a slightly less readable, more error prone and less efficient form of a for (LIST) loop.

Which is exactly the difference I was refering to with: more cumbersome but more adaptable.

If brevity caused my unclarity, please let me know.