Optional type for Objective-C

Optional.h

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface Optional : NSObject

+ (Optional*)with:(id _Nullable)value;
+ (Optional*)with:(id _Nullable)value as:(Class _Nonnull)valueClass;

- (id _Nullable)get;
- (id)getOrElse:(id(^)())elseBlock;

- (Optional*)map:(id(^)(id))mapBlock;
- (Optional*)flatMap:(Optional*(^)(id))flatMapBlock;

- (Optional*)filter:(BOOL(^)(id))filterBlock;

@end

NS_ASSUME_NONNULL_END

Optional.m

#import "Optional.h"

@interface Optional ()

@property (strong, nonatomic, nullable) id value;

@end

@implementation Optional

+ (Optional *)with:(id _Nullable)value
{
  Optional* optional = [Optional new];
  optional.value = value;
  return optional;
}

+ (Optional *)with:(id)value as:(Class)valueClass
{
  if ([value isKindOfClass:valueClass])
  {
    return [Optional with:value];
  }
  return [Optional with:nil];
}

- (id)get
{
  return self.value;
}

- (id)getOrElse:(id  _Nonnull (^)())elseBlock
{
  if (self.value != nil)
  {
    return self.value;
  }
  return elseBlock();
}

- (Optional *)map:(id _Nonnull (^)(id _Nonnull))mapBlock
{
  if (self.value != nil)
  {
    return [Optional with:mapBlock(self.value)];
  }
  return self;
}

- (Optional *)flatMap:(Optional* _Nonnull (^)(id _Nonnull))flatMapBlock
{
  if (self.value != nil)
  {
    return flatMapBlock(self.value);
  }
  return self;
}

- (Optional*)filter:(BOOL (^)(id _Nonnull))filterBlock
{
  return [self flatMap:^Optional*(id value) {
    if (filterBlock(value))
    {
      return self;
    }
    else
    {
      return [Optional with:nil];
    }
  }];
}

@end