[racket] How to get arity of make-object? Found answer

Given that it's easy enough to create a /new/ class on Wednesday that has 3
arguments instead of 2, doesn't it make sense to constrain a given existing
class to have a fixed structure? (just asking)
Maybe it could also allow for some optimizations.

I wonder if such a additional constraint would break anything in the
existing code.

Laurent


On Mon, Jun 9, 2014 at 8:33 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:

> At Fri, 6 Jun 2014 13:23:15 -0400, Asumu Takikawa wrote:
> > On 2014-06-06 06:31:27 +0100, Matthew Flatt wrote:
> > > Sorry for being so late to the discussion, but I agree that something
> > > like `class-constructor-arity` and `class-constructor-arity-includes?`
> > > should be added to `racket/class`.
> >
> > Are those even possible to implement?
> >
> > After all, I can construct a class that has 2 init arguments on
> > Wednesday and has 3 on Friday (by checking the date and then using
> > different `super-new` calls in the branches).
>
> Good point! The `make-object` function doesn't check arities or
> argument names in advance; it has to wait to see what a initialization
> expressions do.
>
> I think we could add a function that reports argument information for
> simple classes, where "simple" is based on the relevant class
> expressions conforming to syntactic constraints. The constraints would
> be a simplified (and documented) variant of the constraints that are
> currently used to determine whether use-before-definition checks are
> needed for accesses of a field's classes.
>
> Is argument information useful enough to do that?
>
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