Perl Shift()->

etlamar has asked for the wisdom of the Perl Monks concerning the following question:

Hi, PerlMonks. I am seeking wisdom about the shift()-> idiom. What does this do? I understand how shift operates in the context of an array, but this form seems to either be dereferencing a hash/array ref or calling a method. Specifically, I found this form of shift in the source code to Geo::Shapefile, e.g.

sub read_shx_header {shift()->read_shx_shp_header('shx',@_);}

Just curious if someone could shed some light on the use of shift in this context

Thanks

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Re: Perl Shift()-> by tobyink (Canon) on Dec 14, 2014 at 21:20 UTC
If you don't specify an array for `shift` and `pop` to operate on, then they operate on `@_` (or if used outside a sub definition, they operate on `@ARGV`). `# Which means that this... sub read_shx_header {shift()->read_shx_shp_header('shx',@_);} # Is a shortcut for writing out... sub read_shx_header { my $self = shift @_; $self->read_shx_shp_header('shx', @_); }` [download] toby döt ink	[reply] [d/l] [select]
Re^2: Perl Shift()-> by etlamar (Novice) on Dec 14, 2014 at 22:33 UTC
Ah!. Thanks for the insight.	[reply]
Re^2: Perl Shift()-> by etlamar (Novice) on Dec 15, 2014 at 02:45 UTC
Thanks much tobyink and GrandFather. The information is very helpful! Best regards.	[reply]
Re: Perl Shift()-> by GrandFather (Saint) on Dec 14, 2014 at 21:18 UTC
`read_shx_header` is a member function. When called the first parameter passed to a member function is `self`. So in that code shift retrieves `self` then calls the member function `read_shx_shp_header` passing 'shx' and the remaining parameters from the original call to `read_shx_header`. In other words, the code is inserting a parameter ('shx') into the front of the parameter list and chaining to another member function to get the actual work done. Perl is the programming world's equivalent of English	[reply] [d/l] [select]