Calling functions whose signature/arguments are only known at runtime

Andrew Whitworth wknight8111 at gmail.com
Wed Mar 17 12:31:26 UTC 2010


On Tue, Mar 16, 2010 at 8:33 PM, Peter Lobsinger <plobsing at gmail.com> wrote:
> On Tue, Mar 16, 2010 at 3:19 PM, Andrew Whitworth <wknight8111 at gmail.com> wrote:
>> Putting arguments into a ResizablePMCArray or Hash and using :flat
>> (Signature "Pf") would similarly resolve the problem.
>
> So we'd have to create a bunch of extra PMCs on every call to pass
> ints, floats, and strings? Ewwww! I know that marshaling between
> calling conventions is inevitably going to be more expensive, but why
> do we make it more expensive when it doesn't have to be?
>
> Also, what if I want to pass a parameter using :flat? Then I can't use
> this trick.

Alternate method is to construct your own CallContext PMC. A
CallContext is created by the invocation anyway, so if you create it
manually and populate it with the values you need, it doesn't create
any extra PMCs.

Creating a CallContext is not difficult, and invoking a method with it
is very simple. Parrot_pcc_invoke_from_sig_object does the trick
magically. After the call, you can get access to the same CallContext
object and use it to extract a variable number of returns as well.

--Andrew Whitworth


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