To give a context, this question is part of my continuing quest to port Python's tqdm style (see Part 1 here: Porting tqdm to Perl). So basically I want to wrap an array or a list of values in a for() loop like this: 

for("some", "el", "ems") {
    ...
}

[download]
with some kind of iterator using this syntax: 
for (wrapper("some", "elems")) {
    # some code
}

[download]

So that for each iteration, as Perl executes some code, each element retrieval also gets to run my code, so I can do something. In the case of tqdm, I want to measure how long some code run so I can give feedback to user on how long the whole loop is going to take. Thus, in essence, adding a progress indicator just by wrapping the list of values given to for().

In Python, this is easy to do because for() already expects an iterator.

In Perl, I can use the array tie mechanism to do this: 

tie @ary, "My::Class", "some", "el", "ems";
for (@ary) {
   some_code($_);
}

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The order of code being executed will be: 

My::Class::TIEARRAY
My::Class::FETCHSIZE
My::Class::FETCH(0) -> "some"
some_code("some")
My::Class::FETCHSIZE
My::Class::FETCH(1) -> "el"
some_code("el")
My::Class::FETCHSIZE
My::Class::FETCH(2) -> "ems"
some_code("ems")


So far so good. However, I also want a nice syntax like in the Python version. Condensing the above syntax to what I want is still not possible:

for (tie @ary, "My::Class", "some", "el", "ems") { ... } # NOPE


This makes for() only loops over a single value, the tied object.


for (do { tie @ary, "My::Class", "some", "el", "ems"; @ary }) { ... } # NOPE


This will FETCH() all elements first before giving them to for().


Any ideas? So far I'm thinking of creating a custom C<for()> function.


EDIT: Added some clarification/additional explanation.

 
 


In reply to Getting for() to accept a tied array in one statement
by perlancar





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