vars in use and require

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

I thought it would be neat to use the perlver module to automatically detect and "use" the minimum version of Perl. But "use" does not seem to accept variables (tried many ways), while "require" takes vars but "Can't locate 5.nnn in @INC". Is this sort of thing even possible? Thanks

#!/usr/bin/perl

use strict;
use warnings;

BEGIN {
  goto DONE unless eval { require Perl::MinimumVersion };
  my $v = Perl::MinimumVersion->new(__FILE__);
  $v = $v->minimum_version;
# use     $v; # no way jose, can't eval either
# require $v; # Can't locate 5.nnn in @INC
# warn    $v; # FYI
  DONE:
}
[download]

Comment on vars in use and require Download Code

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Re: vars in use and require by ikegami (Patriarch) on Sep 22, 2019 at 03:23 UTC
`die "Perl version $v required, only $]\n" if $] < $v;` [download] Update: I had the arguments to the comparison reversed.	[reply] [d/l]
Re: vars in use and require by jcb (Parson) on Sep 21, 2019 at 22:36 UTC
The `use` is evaluated at compile time; try `eval STRING` instead of `eval BLOCK`: `BEGIN { # ... eval q{use $v}; die $@ if $@; }` [download]	[reply] [d/l] [select]
Re^2: vars in use and require by haukex (Archbishop) on Sep 21, 2019 at 23:50 UTC
I was going to suggest something along the lines of `BEGIN { eval "use $]; 1" or die $@ }` instead (Bug in eval in pre-5.14), but it doesn't actually work to enable features: `$ perl -e 'BEGIN { eval "use $]; 1" or die $@ } say "foo"' String found where operator expected at -e line 1, near "say "foo"" (Do you need to predeclare say?) syntax error at -e line 1, near "say "foo"" Execution of -e aborted due to compilation errors.` [download] Because the scope of feature is limited to the lexical scope. So, Anonymous Monk, to echo stevieb: Why do you (think you) need this? (Why try to do something dynamically that is determined statically / at compile time?)	[reply] [d/l] [select]
Re: vars in use and require by stevieb (Canon) on Sep 21, 2019 at 23:08 UTC
Might I ask why you'd want to do this? Is it just a curiosity?	[reply]
Re^2: vars in use and require by Anonymous Monk on Sep 22, 2019 at 06:47 UTC
Because I'm looking at ways to integrate and automate perlver in development and possibly distribution.	[reply]