Objective-C Literals

gistfile1.m

// NSArray Literals
NSArray *array = @[];
NSArray *array = @[@"foo", @"bar", @42];
NSMutableArray *array = [@[] mutableCopy];

// NSDictionary Literals
NSDictionary *dict = @{};
NSDictionary *dict = @{
	@"key": @"value",
	@42: @"int",
	@"float": @3.14f
};
NSMutableDictionary *dict = [@{} mutableCopy];

// NSNumber Literals
NSNumber *number;
number = @23;    // numberWithInt
number = @42u;   // numberWithUnsignedInt
number = @3.14f; // numberWithFloat
number = @YES;   // numberWithBool

// Object Subscripting
NSMutableArray *array = [@[@"foo", @"bar"] mutableCopy];
array[1] = @"foo";
NSMutableDictionary *dict = [@{@"foo": @"bar", @"bar": @"foo"} mutableCopy];
dict[@"foo"] = @"foo";

Source: http://clang.llvm.org/docs/ObjectiveCLiterals.html