ARC Struct Boxable Macros

objc_struct.h

#import <Foundation/Foundation.h>

#define objc_struct_check(__TYPE__, __ACTION__) \
  [__ACTION__.identifier isEqualToString:  @ #__TYPE__] \

#define objc_struct_define \
  typedef struct __attribute__((objc_boxable)) \

#define _objc_boxed_struct_make(__TYPE__, __ARGS__) \
  [[objc_boxed_struct alloc] initWithIdentifier:@ # __TYPE__ \
                                        andData:@(__ARGS__)]; \

#define objc_boxed_struct_make(__STRUCT__) \
  _objc_boxed_struct_make(__typeof(__STRUCT__), __STRUCT__) \

#define objc_struct_get(__TYPE__, __VAR__, __WRAPPER__) \
  __TYPE__ __VAR__; \
  assert(objc_struct_check(__TYPE__, __WRAPPER__)); \
  [__WRAPPER__.boxedStruct getValue:&__VAR__]; \

NS_ASSUME_NONNULL_BEGIN

/// Wraps a dispatch action.
@interface objc_boxed_struct: NSObject
/// The struct identifier (automatically populated by @c objc_boxed_struct_make).
@property(nonatomic, readonly) NSString *identifier;
/// The boxed struct.
/// @note Use The @c objc_struct_check macro to check the action type and
/// @c objc_struct_get to unbox the arguments.
@property(nonatomic, readonly) NSValue *boxedStruct;

/// Don't use the initializer directly.
/// Use @c objc_boxed_struct_make to build a boxed struct.
- (instancetype)initWithIdentifier:(NSString *)identifier andData:(NSValue *)boxedStruct;
@end

NS_ASSUME_NONNULL_END

objc_struct.m

#import "objc_struct.h"

@implementation objc_boxed_struct

- (instancetype)initWithIdentifier:(NSString *)identifier andData:(NSValue *)boxedStruct {
  if (self = [super init]) {
    _identifier = identifier;
    _boxedStruct = boxedStruct;
  }
  return self;
}
@end

test.m

@interface test : XCTestCase
@end

objc_struct_define {
  NSUInteger count;
  NSString *name;
} MyAction1;

objc_struct_define {
  NSNumber *number;
} MyAction2;

@implementation test

- (void)testMacros {
  MyAction1 arg = {
    .count = 0,
    .name = @""
  };
  objc_boxed_struct *userInfo = objc_boxed_struct_make(arg);

  if (objc_struct_check(MyAction2, userInfo)) {
    XCTFail();
  } else if (objc_struct_check(MyAction1, userInfo)) {
    objc_struct_get(MyAction1, arg2, userInfo);
    XCTAssert(arg2.count == arg.count);
    XCTAssert([arg2.name isEqualToString:arg.name]);
  }
}

@end