Cool Things in Perl 6
Yeah, Perl 6 is going to allow us to do very interesting things. Given this code:
use v6;
subset Filename of Str where { $_ ~~ :f };
sub foo (Filename $name) {
say "Houston, we have a filename: $name";
}
my Filename $foo = $*EXECUTABLE_NAME;
foo($foo);
foo($*EXECUTABLE_NAME);
foo('no_such_file');We get this output:
Houston, we have a filename: /Users/ovid/bin/perl6 Houston, we have a filename: /Users/ovid/bin/perl6 Constraint type check failed for parameter '$name' in Main (file src/gen_setting.pm, line 324)
Obviously the error message needs some work (and I would love to be able to generate custom error messages for subsets), but proper use of subsets are going to save a lot of code and prevent a lot of errors.
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You can simply use multi for the error message.
One multi-call of foo uses the Filename type, another accepts Str. If it falls through to the string case, it didn't match the Filename subset.