This is another spin-off from the 'Exposing the Garbage Collector'
thread. Here is an enhanced version.
I wonder how the generic, lexically scoped invocant/owner is called.
I propose to call it $/ (other option is to call it $&)and let the
former topicalizer become block owners and $_ the block topic that flows
into blocks from further outside if not explicitly bound with -> like:
$topic := Some.new;
$_ := $topic;
for @objects { .action } # call on $/ from @objects with $_ := $topic
# in all loops
@objects».action; # same for single action syntax
# but
for @objects -> { .action } # means $/.action($/) because
# $_ bound to dynamic block owner;
# but usefull for methods that don't
# use the topic, in particular accessors
# and mutators
# same as sub call
for @objects -> { action } # means action($/) because $_ := $/
# but $/ is there if action is of
# type Method
# but the $. @. %. and &. are bound through $?SELF
# in particular
for @objects -> { &.action } # subref curried on invocant
This implies that a .action means name lookup of 'action' while
&.action is an onboard method of $?SELF. This latter case is
typically implemented with a vtbl lookup.
The only drawback I see is, that the careless method programmer could be
caugth in an endless .action loop if .action invokes .action explicitly
on $_ where $_ := $/ from the outside. The same endless loop could of
course be achieved with a free standing .action but that looks more like
intention.
With the lurking pitfalls an occasional check of $_ =:= $?SELF and
$/ =:= $_ seems advisable and indicates that the invocant wasn't
exchanged midway :)
Same with other block topicalizers/owners
given $x {...} # topic untouched, but $/ := $x
given $x -> {...} # $_ := $x as well
But
if $x {...} # $/ and $_ untouched
if $x -> {...} # $_ := $x (non boolean value)
One more interessting thing is that in exception handlers all three
variables $!, $/ and $_ are in scope. This might allow to resume where
the exception occurred after the cause was fixed e.g. by loading or
generating some code, some revamping or other &DEEP_MAGIC. Hmm, debug
exceptions come to mind...
--
TSa (Thomas Sandlaß)
