In the spirit of TMTOWTDI, I would use the following idiom: 
my %ext = ( ... );
...

my $method = $ext{'JPEG'};
print $image->$method;
...

[download]

That makes it clearer what the point of the variable is - it's a method name.

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Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

In reply to Re: subroutine referencing by dragonchild
in thread subroutine referencing by imcsk8

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