Yet Another Perl Switch Statement
source link: https://dev.to/matthewpersico/yet-another-perl-switch-statement-54h3
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Yet Another Perl Switch Statement
I am in the middle of a project at my job where we are converting some Perl to Python :-(. In the conversion I was explaining this invocation of a switch statement:
for (ref($thing)) {
/ARRAY/ && do {
some_array_thing($thing);
last;
};
/LIST/ && do {
some_list_thing($thing);
last;
};
## default;
some_scalar_thing($thing);
}
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After explaining how the for statement sets $_, I was asked, "Why not just set $_?"
Indeed, why not? You can play with the following code here: http://tpcg.io/KN9H82
use strict;
use warnings;
{
local $_ = 'foo';
/bar/ && do { print 'we got bar'; last };
/foo/ && do { print 'we got foo'; last };
/eek/ && do { print 'we got eek'; last };
print 'we dropped through';
}
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with output
we got foo
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So, my questions are:
- Why have I never seen this in any discussion of Perl's
switchsynonyms? - Is there any inherent problem with this?
Discussion (4)
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That’s exactly what for does, except it’s lexical instead of local.
Perl v5.10 introduced support for explicitly lexical $_, but it was removed in v5.24 after being relegated to experimental status in v5.18. (See that last link for the issues it introduced.)
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Right, but the Python person I was talking to said that for their reading, the explicit assignment to $_ made a lot more sense to him than implying it from a for loop. Again, a Python person, "explicit is better than implicit". However, to be honest, I like explicit setting of $_ better than a for loop. So much cleaner IFF you really are using only one value. In fact, I would improve this code with
SWITCH: {
local $_ = 'foo';
...
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And I think I avoid the lexical issues with the local modifier, yes?
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Sure, use a label and then the last statement of your conditions can say last SWITCH;.
If you like your Perl more “Pythonic” then go for it. Personally I prefer to adopt language idioms rather than adapt one language to another. Similar arguments have occurred about C-style for ( ; ; ) loops vs. foreach loops that eschew an index variable when it’s not necessary.
There’s an old saying: “You can write FORTRAN in any language.” The Sapir-Whorf hypothesis says that language influences thought. Limiting yourself to the idioms of one language means limiting yourself to solutions that can be expressed in it, and that doesn’t make sense if you’re actually using a different language.
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I was going to say that you can't get fall-through with /match/ && do {...}, but then I started thinking "When was the last time I wanted fall-through? That wasn't parlor-trick code?"
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