Make PLBlockIMP drop in compatible on iOS 4 and 5

.gitignore

@@ -0,0 +1,8 @@
+*.mode1
+*.mode1v3
+*.mode2v3
+*.perspective
+*.perspectivev3
+*.pbxuser
+project.xcworkspace
+xcuserdata

Source/blockimp.c

@@ -31,6 +31,41 @@
 
 #include <stdio.h>
 #include <Block.h>
+#include <dispatch/dispatch.h>
+#include <dlfcn.h>
+
+// Convenience for falling through to the system implementation.
+static BOOL fallthroughEnabled = YES;
+
+#define NEXT(name, ...) do { \
+static dispatch_once_t fptrOnce; \
+static __typeof__(&name) fptr; \
+dispatch_once(&fptrOnce, ^{ fptr = dlsym(RTLD_NEXT, #name); });\
+if (fallthroughEnabled && fptr != NULL) \
+return fptr(__VA_ARGS__); \
+} while(0)
+
+void PLBlockIMPSetFallthroughEnabled(BOOL enabled) {
+    fallthroughEnabled = enabled;
+}
+
+IMP imp_implementationWithBlock(PLObjectPtr block) {
+    NEXT(imp_implementationWithBlock, block);
+
+    return pl_imp_implementationWithBlock(block);
+}
+
+PLObjectPtr imp_getBlock(IMP anImp) {
+    NEXT(imp_getBlock, anImp);
+
+    return pl_imp_getBlock(anImp);
+}
+
+BOOL imp_removeBlock(IMP anImp) {
+    NEXT(imp_removeBlock, anImp);
+
+    return imp_removeBlock(anImp);
+}
 
 #pragma mark Trampolines
 
@@ -47,12 +82,6 @@ static pl_trampoline_table *blockimp_table = NULL;
  * 
  */
 IMP pl_imp_implementationWithBlock (void *block) {
-#if SUPPORT_APPLE_FALLBACK
-    /* Prefer Apple's implementation */
-    if (&imp_implementationWithBlock != NULL)
-        return imp_implementationWithBlock(block);
-#endif
-
     /* Allocate the appropriate trampoline type. */
     pl_trampoline *tramp;
     struct Block_layout *bl = block;
@@ -75,13 +104,6 @@ IMP pl_imp_implementationWithBlock (void *block) {
  *
  */
 void *pl_imp_getBlock(IMP anImp) {
-#if SUPPORT_APPLE_FALLBACK
-    /* Prefer Apple's implementation */
-    if (&imp_getBlock != NULL) {
-        return imp_getBlock(anImp);
-    }
-#endif
-
     /* Fetch the config data and return the block reference. */
     void **config = pl_trampoline_data_ptr(anImp);
     return config[0];
@@ -91,12 +113,6 @@ void *pl_imp_getBlock(IMP anImp) {
  *
  */
 BOOL pl_imp_removeBlock(IMP anImp) {
-#if SUPPORT_APPLE_FALLBACK
-    /* Prefer Apple's implementation */
-    if (&imp_removeBlock != NULL)
-        return imp_removeBlock(anImp);
-#endif
-
     /* Fetch the config data */
     void **config = pl_trampoline_data_ptr(anImp);
     struct Block_layout *bl = config[0];

Source/blockimp.h

@@ -25,7 +25,16 @@
  */
 
 #include <objc/runtime.h>
+#include <Availability.h>
 
-extern IMP pl_imp_implementationWithBlock(void *block);
-extern void *pl_imp_getBlock(IMP anImp);
-extern BOOL pl_imp_removeBlock(IMP anImp);
+#if defined (__MAC_10_8) || defined (__IPHONE_6_0)
+    typedef id PLObjectPtr;
+#else
+    typedef void *PLObjectPtr;
+#endif
+
+OBJC_EXPORT IMP imp_implementationWithBlock(PLObjectPtr block);
+OBJC_EXPORT PLObjectPtr imp_getBlock(IMP anImp);
+OBJC_EXPORT BOOL imp_removeBlock(IMP anImp);
+
+OBJC_EXPORT void PLBlockIMPSetFallthroughEnabled(BOOL enabled);

Source/blockimp_private.h

@@ -41,16 +41,6 @@
 # error Unknown Architecture
 #endif
 
-#pragma mark Fallback Support
-
-// if 1, we attempt to use Apple's official implementations
-#define SUPPORT_APPLE_FALLBACK 0
-#if SUPPORT_APPLE_FALLBACK
-extern IMP imp_implementationWithBlock(void *block) WEAK_IMPORT_ATTRIBUTE;
-extern void *imp_getBlock(IMP anImp) WEAK_IMPORT_ATTRIBUTE;
-extern BOOL imp_removeBlock(IMP anImp) WEAK_IMPORT_ATTRIBUTE;
-#endif
-
 /*
  * Block Flags
  */
@@ -132,4 +122,8 @@ struct Block_layout {
     struct Block_descriptor *descriptor;
 
     // imported variables
-};
+};
+
+IMP pl_imp_implementationWithBlock(void *block);
+void *pl_imp_getBlock(IMP anImp);
+BOOL pl_imp_removeBlock(IMP anImp);

Source/blockimp_tests.m

@@ -27,6 +27,10 @@
 #import "GTMSenTestCase.h"
 #import "blockimp.h"
 
+IMP pl_imp_implementationWithBlock (void *block);
+void *pl_imp_getBlock(IMP anImp);
+BOOL pl_imp_removeBlock(IMP anImp);
+
 @interface BlockIMPTests : SenTestCase @end
 
 /**