Re: [Patch v18 4/4] Add xmethod support to the Python API

[Doug Evans <dje at google dot com>]

On Wed, May 28, 2014 at 12:12 PM, Siva Chandra <sivachandra@google.com> wrote:
> On Tue, May 27, 2014 at 10:41 PM, Doug Evans <xdje42@gmail.com> wrote:
>> Another thing occurs to me.
>> Pretty-printers are invoked, initially, via __call__, not via a "print"
>> method or some such.
>> It would be more python-esque if XMethodMatcher.match was renamed __call__
>> and XMethodWorker.invoke was renamed __call__.
>
> While I agree XMethodWorker.invoke can be removed and we could make
> XMethodWorker a callable, I am not sure we want to make XMethodMatcher
> a callable. I know pretty printers are callables but do not know the
> reason why they are so (probably because there is an old way and a new
> way of writing pretty printers and both have to be supported). For me,
> a __call__ method in Python is like operator() in C++ which I feel
> should be used only if it is meaningful to make the objects callable.
> Even for the XMethodWorker, I preferred a method 'invoke' over making
> workers callables because they are named as workers and not as
> methods. The only reason I had to bring in the notion of XMethods
> (which are used only for enable/disable) and XMethodWorker is because
> I had to ape the pretty printer setup. I propose a slightly different
> design here which does not ape the pretty printers completely but
> makes it less confusing:
>
> 1. Have XMethodMatchers with a method named 'match'. Matchers have an
> attribute 'enabled'. GDB invokes the 'match' method on registered
> matchers if they are enabled. On a match, the matcher returns a
> sequence of matching and enabled XMethods. See #2 to know what
> XMethods are. An XMethodMatcher also has an attribute 'method', which
> is a sequence of XMethods the matcher manages. This provides a way to
> enable/disable individual XMethods from enable/disable commands.
> 2. Have XMethods which are callables, but also have a method
> 'get_arg_types'. XMethods also have an 'enabled' attribute to indicate
> whether they are enabled or not. GDB calls an XMethod (they are
> callables) if it determines that the XMethod is the best overload
> match.

By analogy, what this does is merge SubPrettyPrinter with the
pretty-printer worker object.

FAOD,

XMethodMatcher
  attributes: name, enabled, methods, match

XMethod
  attributes: name, enabled, get_arg_types, __call__

"works for me"