How to implement chainable syntax with objective-c? - objective-c

Question

For example:
someObject.a.and.b.offset(5)
In objecitive-c, we know that a Class can have properties and methods, how to mix them to implement chainable syntax? How to design?

Answer 1

Have a look at this library: Underscore Library
Actually what it does it to return the same object you are operating on, so you can call more methods on the object (chaining them). Also block properties are used in order to obtain this syntax.
Here is an example from the website:
NSArray *tweets = Underscore.array(results)
// Let's make sure that we only operate on NSDictionaries, you never
// know with these APIs ;-)
.filter(Underscore.isDictionary)
// Remove all tweets that are in English
.reject(^BOOL (NSDictionary *tweet) {
return [tweet[#"iso_language_code"] isEqualToString:#"en"];
})
// Create a simple string representation for every tweet
.map(^NSString *(NSDictionary *tweet) {
NSString *name = tweet[#"from_user_name"];
NSString *text = tweet[#"text"];
return [NSString stringWithFormat:#"%#: %#", name, text];
})
.unwrap;
You might want to look at this SO-Thread aswell.
There is another library shown which implements this behaviour.

Answer 2

Here is my note. For example:
#class ClassB;
#interface ClassA : NSObject
//1. we define some the block properties
#property(nonatomic, readonly) ClassA *(^aaa)(BOOL enable);
#property(nonatomic, readonly) ClassA *(^bbb)(NSString* str);
#property(nonatomic, readonly) ClassB *(^ccc)(NSString* str);
#implement ClassA
//2. we implement these blocks, and remember the type of return value, it's important to chain next block
- (ClassA *(^)(BOOL))aaa
{
return ^(BOOL enable) {
//code
if (enable) {
NSLog(#"ClassA yes");
} else {
NSLog(#"ClassA no");
}
return self;
}
}
- (ClassA *(^)(NSString *))bbb
{
return ^(NSString *str)) {
//code
NSLog(#"%#", str);
return self;
}
}
// Here returns a instance which is kind of ClassB, then we can chain ClassB's block.
// See below .ccc(#"Objective-C").ddd(NO)
- (ClassB * (^)(NSString *))ccc
{
return ^(NSString *str) {
//code
NSLog(#"%#", str);
ClassB* b = [[ClassB alloc] initWithString:ccc];
return b;
}
}
//------------------------------------------
#interface ClassB : NSObject
#property(nonatomic, readonly) ClassB *(^ddd)(BOOL enable);
- (id)initWithString:(NSString *)str;
#implement ClassB
- (ClassB *(^)(BOOL))ddd
{
return ^(BOOL enable) {
//code
if (enable) {
NSLog(#"ClassB yes");
} else {
NSLog(#"ClassB no");
}
return self;
}
}
// At last, we can do it like this------------------------------------------
id a = [ClassA new];
a.aaa(YES).bbb(#"HelloWorld!").ccc(#"Objective-C").ddd(NO)