'' examples/manual/libraries/ffi/closures.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'libffi'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=ExtLibFfi
'' --------

#include "ffi.bi"

' Acts like puts with the file given at time of enclosure. 
Sub Printer cdecl(ByVal cif As ffi_cif Ptr, ByVal ret As Any Ptr, ByVal args As Any Ptr Ptr, ByVal File As Any Ptr)
	Write #*CPtr(Integer Ptr, file), **CPtr(ZString Ptr Ptr, args[0])
	*CPtr(UInteger Ptr, ret) = 42
End Sub

' Allocate the closure and function binding
Dim PrinterBinding As Function(ByVal s As ZString Ptr) As Integer
Dim closure As ffi_closure Ptr 
closure = ffi_closure_alloc(SizeOf(ffi_closure), @PrinterBinding)

If closure <> 0 Then
	' Initialize the argument info vector
	Dim args(0 To 0) As ffi_type Ptr = {@ffi_type_pointer}
	
	' Initialize the call interface
	Dim cif As ffi_cif
	Dim prep_result As ffi_status = ffi_prep_cif( _
		@cif,            _ ' call interface object
		FFI_DEFAULT_ABI, _ ' binary interface type
		1,               _ ' number of arguments
		@ffi_type_uint,  _ ' return type
		@args(0)         _ ' arguments
	) 
	If prep_result = FFI_OK Then
		' Open console file to send to PrinterBinding as user data
		Dim ConsoleFile As Integer = FreeFile()
		Open Cons For Output As ConsoleFile
		
		' Initialize the closure, setting user data to the console file
		prep_result = ffi_prep_closure_loc( _
			closure,         _ ' closure object
			@cif,            _ ' call interface object
			@Printer,        _ ' actual closure function
			@ConsoleFile,    _ ' user data, our console file #
			PrinterBinding   _ ' pointer to binding
		)
		If prep_result = FFI_OK Then
			' Call binding as a natural function call
			Dim Result As Integer
			Result = PrinterBinding("Hello World!")
			Print Using "Returned &"; Result
		End If
		
		Close ConsoleFile
	End If
End If

' Clean up
ffi_closure_free(closure)
