Why use a "do {} if" block in Perl?

Question

While browsing CPAN, I came across a block of code in this module that stumped me.

sub import {
  for my $mod (keys %INC) {
    do {
      delete $INC{$mod};
      $mod =~ s/\.pm$//; $mod =~ s/\//::/g;
      delete_package($mod);
    } if $mod =~ m/^SOAP/;
  }
}

Why would the author use a do {} if block instead of a regular if block?

Answer 1

Because they feel like it. There's no real difference. Perl has like a dozen ways to do everything. It's just the way the language is.

Answer 2

One difference is that do { ... } returns a value whereas an if statement doesn't (although see the comments below.)

E.g.:

my $x = 3;
my $z = do { warn "in the do block"; 10 } if $x == 3;

You can accomplish almost the same thing with the ternary operator, although you can't sequence statements inside the branches of the ternary operator.

Answer 3

To me, it seems like a way to emphasize the code inside the if more than the if condition itself.

Answer 4

The author wanted to use the if at the end, but it has to be at the end of one statement not many. A do {} is one statement, so that will work.

Personally, I would use an if statement, but it is a matter of taste whether the emphasis should be on the action or the condition. In this case the author chose to emphasize the action.