See https://docs.perl6.org/type/Signature#Constraining_defined_and_undefined_values
If I say "my Int $x", $x is now an Int, but an undefined Int. If I say "my Int $x = 42", $x is an Int, but set to a defined value, 42. Both are Int: say 42 ~~ Int; # OUTPUT: «True» say Int ~~ Int; # OUTPUT: «True» There are three type constraint suffixes you can add -- :D (defined), :U (undefined) or :_ (defined or undefined) # Checking a type object say Int ~~ Any:D; # OUTPUT: «False» say Int ~~ Any:U; # OUTPUT: «True» say Int ~~ Any:_; # OUTPUT: «True» # Checking an object instance say 42 ~~ Any:D; # OUTPUT: «True» say 42 ~~ Any:U; # OUTPUT: «False» say 42 ~~ Any:_; # OUTPUT: «True» On Fri, Sep 14, 2018 at 7:08 AM Todd Chester <toddandma...@zoho.com> wrote: > > > On 09/14/2018 04:01 AM, Simon Proctor wrote: > > :D is a type constraint requiring an instantiated (or defined) object of > > the given type (or a subtype of it). > > > > :U is a type constraint saying you have a container specified for the > > given type that hasn't been instantiated. > > Hi Simon, > > Your went over my head. What the heck is "instantiated"? > > https://www.dictionary.com/browse/instantiate > verb (used with object), in·stan·ti·at·ed, in·stan·ti·at·ing. > > to provide an instance of or concrete evidence in support > of (a theory, concept, claim, or the like). > > I am not connecting the dots. > > Is there a list of these guys somewhere, or are these the only two? > > -T >
