I don't think `ffi/unsafe` can generate that kind of wrapper for you.
I'd write something like this:
(define-vulkan vkEnumerateInstanceLayerProperties/private
(_fun (o0 : (_ptr io _uint32_t))
_pointer
-> (r : _VkResult)
-> (begin
(check-vkResult r 'vkEnumerateInstanceLayerProperties)
o0))
#:c-id vkEnumerateInstanceLayerProperties)
(define (vkEnumerateInstanceLayerProperties)
(define len (vkEnumerateInstanceLayerProperties/private 0 #f))
(define props (malloc _VkLayerProperties len))
(define new-len (vkEnumerateInstanceLayerProperties/private len props))
(values new-len props))
At Sun, 20 Oct 2019 03:47:52 +0000, Sage Gerard wrote:
> Consider the following C++ that calls a function once to learn how much it
> should allocate for a vector, and again to populate said vector.
>
> uint32_t count;
>
> vkEnumerateInstanceLayerProperties(&count, NULL);
>
> std::vector<VkLayerProperties> properties(count);
>
> vkEnumerateInstanceLayerProperties(&count, properties.data());
>
> Below is my generated signature so far. The docs for
> [_list](https://docs.racket-lang.org/foreign/foreign_procedures.html?q=_fun#%28
> form._%28%28lib._ffi%2Funsafe..rkt%29.__list%29%29) shows similar examples,
> but they assume either the length of the vector is known in advance.
>
> How would I make a custom function type to manage both o1 and o0 values with
> the garbage collector, call the function twice as described, and return the
> value for o1 in a single call?
>
> (define-vulkan vkEnumerateInstanceLayerProperties
> (_fun (o0 : (_ptr o _uint32_t))
> (o1 : (_ptr o _VkLayerProperties))
> -> (r : _VkResult)
> -> (begin (check-vkResult r (quote
> vkEnumerateInstanceLayerProperties))
> (values o0 o1))))
>
> ~slg
>
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