A much improved and refined sub VERSION() for the implicit approach. 


sub VERSION {
    my ($module, $version) = @_;
    return $VERSION unless $version; # satisfy UNIVERSAL::VERSION()

    do { require File::Spec;
         require File::Basename;
        my $file = File::Spec->catfile( split /::/, $module ) . ".pm";
         my $dir;
        $dir = File::Basename::dirname( $dir || $INC{$file} ) 
                     for 0 .. $module =~ /::/g;

        for my $dir ( local @INC = grep { !/^$dir$/ && -e File::Spec->
+catfile( $_, $file ) } @INC ) {
            open MOD, "<", File::Spec->catfile( $dir, $file ) or warn 
+"$@";
            grep {
                /(.*VERSION.*)/ 
                and eval "eval '$1' == $version" 
                and do {
                    delete $INC{$file};
                    eval " require $module; $module->VERSION " == $ver
+sion and do return $version ;
                    shift @INC;
                }
            } <MOD>;
        }

        require Carp;
        Carp::croak(" Loading $module ($version) failed. ");

    } unless ($version == $VERSION);
}

[download]
A loader hook for @INC for explicit version control, basically just the above modified slightly. 
BEGIN {
    sub my_use {
        my ($arg_ref, $module) = @_;
        my $version;
        local @INC;
        (undef, $version, @INC) = @$arg_ref;
        require File::Spec;
        for my $dir ( grep { -e File::Spec->catfile( $_, $module ) } @
+INC ) {
            my $file = File::Spec->catfile( $dir, $module );
            open MOD, "<", $file or warn "failed opening $file : $@";
            grep {
                /(?:VERSION\s*=(.*))/
                and eval "eval '$1' || 0" == $version
                and do {
                    open my $fh, "<", $file or warn "open $file failed
+ : $@";
                    close MOD;
                    return $fh;
                }
            } <MOD>;
        }

    }
   {
    local @INC = [ \&my_use, "1.03", qw|a b c|, @INC ];
    eval "use strict";
   }
   {
    local @INC = [ \&my_use, "5.01", @INC, qw|a b c|];
    eval "use Foo::Bar";
   }
}

[download]
There's bound to be room for correction and improvement, especially to creating a simple and elegant data structure to house information about module and version numbers.

In reply to Re^4: BEGIN and compile-time by Firefly258
in thread BEGIN and compile-time by jbert

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