Having trouble porting code between systems.

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

I have a piece of code that uses; @arr = sort{ %{ $a }{"tag"} <=> %{ $b }{"tag"} } @arr; and works fine on strawberry perl (windows 12 server). The same line causes a syntax error in v5.16.3 Any ideas? Thanks

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Re: Having trouble porting code between systems. by choroba (Cardinal) on Feb 05, 2019 at 22:33 UTC
In ancient Perl versions, it was possible to use `%{ $a }{"tag"}` instead of `${$a}{"tag"}` which is usually written with the dereference arrow as `$a->{tag}`. In later versions, the syntax became an error, and in the recent versions, it was introduced for key/value hash slices, where `%{ $hash_ref }{ 'key1', 'key2' }` returns the corresponding key value pairs, e.g. `qw( key1 value1 key2 value2 )`. So, replace the line with any of `@arr = sort{ ${ $a }{"tag"} <=> ${ $b }{"tag"} } @arr; @arr = sort{ $$a{"tag"} <=> $$b{"tag"} } @arr; @arr = sort { $a->{tag} <=> $b->{tag} } @arr;` [download] Update: Interestingly, the old syntax will start working in the recent Perl versions again, because `%{ $a }{tag}` will return both the string "tag" and its corresponding value, but `<=>` enforces scalar context to its arguments, so only the last one will be used, i.e. the value of the tag. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]

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Re: Having trouble porting code between systems.
by choroba (Cardinal) on Feb 05, 2019 at 22:33 UTC

%{ $a }{"tag"}

${$a}{"tag"}

$a->{tag}

%{ $hash_ref }{ 'key1', 'key2' }

qw( key1 value1 key2 value2 )

So, replace the line with any of

@arr = sort{ ${ $a }{"tag"} <=> ${ $b }{"tag"} } @arr;
@arr = sort{ $$a{"tag"} <=> $$b{"tag"} } @arr;
@arr = sort { $a->{tag} <=> $b->{tag} } @arr;
[download]

Update: Interestingly, the old syntax will start working in the recent Perl versions again, because %{ $a }{tag} will return both the string "tag" and its corresponding value, but <=> enforces scalar context to its arguments, so only the last one will be used, i.e. the value of the tag.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

[reply]
[d/l]
[select]