[cpp][4.3-beta] failed to compile with "SPINE_USE_STD_FUNCTION" defined

[pbk20191]

after commit 51410a5
can not compile spine-cpp with #define SPINE_USE_STD_FUNCTION

because signature is not correct for std::function version

[lukeeingram]

Hello,

Can you provide some more information about how you're trying to compile spine-cpp and where it's erroring out? Are you using one of our integrations, like spine-sdl or spine-flutter?

[pbk20191]

I'm porting spine-cpp using Objective-c++ which can mix Objective-c and C++.
So that I can expose dedicated features as Objective-C interface which can be bridged to Swift.
I use SPINE_USE_STD_FUNCTION so that cpp can capture Objective-C Block (Kind of Cpp lambda but based on libobjc.dylib, Clang-Block)
---- Swift/Objective-C can create and call Block(Clang/Objective-C block) but can not create or call C++ std::function.

// this is block_helper.mm file which compiles as objective-c++,  using objctive-c++ compiler with objc_arc
// otherwise `block` needs to be manually reference counted using Block_copy, Block_release
// below condition is always true in standard apple platform sdk (macOS, watchOS, visionOS, iOS, tvOS)
// without __has_feature(objc_arc) block needs to be managed using Block_copy, Block_release
#ifdef SPINE_USE_STD_FUNCTION
#if __OBJC__ && __has_feature(objc_arc) && __BLOCKS__ 
#include <Block.h>
typedef void (^SpineAnimationCallbackBlock)(spine_animation_state _Nonnull state, spine_event_type type, spine_track_entry _Nonnull entry, spine_event _Nullable event);

void spine_track_entry_set_block(spine_track_entry _Nonnull entry, SpineAnimationCallbackBlock _Nullable block) {
    if (!entry) {
        return;
    }
    auto self = reinterpret_cast<spine::TrackEntry *>(entry);
    if (!block) {
        self->setListener(0);
    } else {
        self->setListener([block](spine::AnimationState* state, spine::EventType type, spine::TrackEntry *trackEntry, spine::Event *event) {
    
            @autoreleasepool {
                block(
                      reinterpret_cast<spine_animation_state>(state),
                      static_cast<spine_event_type>(type),
                      reinterpret_cast<spine_track_entry>(trackEntry),
                      reinterpret_cast<spine_event>(event)
                      );
            }
        });
    }
}

void spine_animation_state_set_block(spine_animation_state _Nonnull state, SpineAnimationCallbackBlock _Nullable block) {
    if (!state) {
        return;
    }
    auto self = reinterpret_cast<spine::AnimationState *>(state);
    if (!block) {
        self->setListener(0);
    } else {
        self->setListener([block](spine::AnimationState* state, spine::EventType type, spine::TrackEntry *trackEntry, spine::Event *event) {
            @autoreleasepool {
                block(
                      reinterpret_cast<spine_animation_state>(state),
                      static_cast<spine_event_type>(type),
                      reinterpret_cast<spine_track_entry>(trackEntry),
                      reinterpret_cast<spine_event>(event)
                      );
            }
        });
    }
}

#endif
#endif

Above code block do their jobs before commit 51410a5

now the compiler fails with following error

Build SpineRuntime_2025-09-04T11-34-23.txt

because the arguments are not same with std::function (4 argument) and c-function pointer (5-arguments) version.