Re: default parameters in methods
Larry Wall larry-at-wall.org |Perl 6| wrote: All default expressions to any parameter are defined to run in the context that assumes any parameters to their left are already bound, so you may safely depend on self already being set. OK, so there is no technical reason why it can't work that way. But, self the keyword is not $self the parameter (it only works in methods), and there are issues of trust. So I need to describe it properly. --John
default parameters in methods
It is not specified in the Synopses as I recall, but I believe that this is useful enough that it must be made to work: method bytes (Encoding :$encoding = .encoding) returns Int or even method bytes (Encoding :$encoding = self!encoding) returns Int That is, a named-only parameter, which may be used as an optional adverb or extra parameter to affect details of the function, should default to a pre-set value inside the instance. If this is not allowed, the beginning of the method would always have to check for defaults. That should be automatic. And it documents the situation nicely in the signature, without further explanation that if the parameter is not supplied... This means that the default arguments run inside the context of the method call, and can do anything that you would expect from their lexical position. --John
Re: default parameters in methods
On Fri, Apr 11, 2008 at 03:35:37AM -, John M. Dlugosz wrote: : It is not specified in the Synopses as I recall, but I believe that this is useful enough that it must be made to work: : :method bytes (Encoding :$encoding = .encoding) :returns Int : : or even : :method bytes (Encoding :$encoding = self!encoding) :returns Int : : That is, a named-only parameter, which may be used as an optional adverb or extra parameter to affect details of the function, should default to a pre-set value inside the instance. : : If this is not allowed, the beginning of the method would always have to check for defaults. That should be automatic. And it documents the situation nicely in the signature, without further explanation that if the parameter is not supplied... : : This means that the default arguments run inside the context of the method call, and can do anything that you would expect from their lexical position. All default expressions to any parameter are defined to run in the context that assumes any parameters to their left are already bound, so you may safely depend on self already being set. Larry
