2015-02-22 0:06 GMT+01:00 Max Leske <[email protected]>:
> Hi.
>
> I have a situation with libgit2 where the function I need to call is a
> field in a struct (the field gets populated with different functions with
> the same signature depending on certain conditions).
>
> I’m facing two problems now:
> 1. how do I define a function as the field type of an NBExternalStructure?
>
Athens creates a structure with callbacks as a surface plugin for the
bitblter (SQSurfaceDispatch).
But this is a structur with functions (generated with NB) that are called
"from the outside"
> 2. how can I call the function?
>
I don't know of any example in the image, where we are calling a function
defined in a struct.
Maybe you can extend NBFFICallout to generate a call from a function spec +
function address
NBFFICallout>>#generateCall:module: does this, it generates a call from a
function spec and and
address loockuped in a module, maybe you can do something similiar, but use
the function address from
the structure isntead of calling nbGetSymbolAddress:module:
>
> I’ve tried using callbacks as field types. That works as far as I can
> access the functions by pointer. But how would I then call that function?
> I’ve looked at NBNativeFunction and NBNativeFunctionGen but I can’t see
> how I should use either of those to make a plain call.
>
> Here’s a more precise description of my problem:
>
> writepack := LG2GitOdbWritepackS new.
> … “initialize the struct externally”
>
> “now call the function ‘commit’ and pass the arguments (this is how I
> imagine it could work…)"
> writepack commit
> value: writepack
> value: anotherStruct.
>
>
> Needed struct fields:
>
> backend: git_odb_backend *
> append: int (*)(git_odb_writepack *, const void *, size_t,
> git_transfer_progress *)
> commit: int (*)(git_odb_writepack *, git_transfer_progress
> *)
> free: void (*)(git_odb_writepack *)
>
>
For what is this needed? Do you want to write your own git backend?
I find this strange. I only know of two use cases for function pointers in
a structs.
1. to define the callbacks (like athens does it for the SQSurfaceDispatch).
But we only define the functions and don't call them.
2. a library defines a public api and delegates the implementation to
different backends, but structure and backend functions
are hidden. Users of the library don't call them.
>
> My current (ad hoc) struct fields:
>
> fieldsDesc
> ^#(
> LG2GitOdbO backend;
> LG2WritePackAppendCb append;
> LG2WritePackCommitCb commit;
> LG2WritePackFreeCb free;
> )
>
>
> I’d even be happy if I have to implement a method on LG2GitOdbWritepackS
> for every function call (e.g. “writepack commit: arg1 and: arg2”) but how
> would I make the call?
>
> Any ideas?
> Max
>
