linjunpop/Objective-C-for-Rubyist.md

## Objective-C-for-Rubyist.md

      
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              Objective-C-for-Rubyist.md
            
          
    Objective-C for Rubyist

Basic Syntax

Message

[you say:@"Hello."];
Ruby:
you.say('Hello')
In particular, Objective-C’s:
[apple performSelector:@selector(eat:)
                        withObject:camembert]; // Equivalent to [apple eat:camembert];
Would be equivalent to Ruby’s:
apple.send(:eat, camembert)
Sadly, we CANNOT use
[apple performSelector:@selector(@"eat:")
                        withObject:camembert];
Another way:
id objc_msgSend(id theReceiver, SEL theSelector, ...)
Protocal

@protocal Talking

- (void)say:(NSString *)word;

@end

// Miao.h
@interface Miao<Talking>
@end

// Miao.m
@implement Miao
- (void)say:(NSString *)word {
  NSLog(@"Hi");
}
@end
Property

// Interface
#import <Foundation/Foundation.h>

@interface UserModel : NSObject

@property (retain) NSString* name;

@end

// Implementation
#import "UserModel.h"

@implementation UserModel

@synthesize name;

@end
Set age to be available with read and write access (getter and setter)
we want the argument to be assigned to the property.
Ruby:
attr_accessor, attr_reader, attr_writer
Initialize

[[Foo alloc] init]

Camembert *camembert = [[Camembert alloc] initWithAge:3 smell:someSmell];
Ruby:
class Object
  def self.new(*args)
    self.alloc.initialize(*args)
  end

  def initialize
  end
end
Duck typing

id you = [[Superman alloc] init];
id point to any object.
Ruby:
"foo".respond_to?(:to_s)
#=> true

1.respond_to?(:to_s)
#=> true
Interface

Header file: UserModel.h
#import <Foundation/Foundation.h>

@interface UserModel : NSObject

+ (NSMutableArray *)all;

@end
Implementation file: UserModel.m
#import "UserModel.h"

@implementation UserModel

+ (NSMutableArray *)all {
    // ...
}

@end
Monkey patching (categories)

"A category allows you to add methods to an existing class—even to one for which you do not have the source."
#import <Foundation/Foundation.h>
 
@interface AClass (ACategory)
 
@end
File: NSDate+Formatting.h
#import <Foundation/Foundation.h>
 
@interface NSDate (Formatting)
 
- (NSString*) timeAgoInWords;
 
@end

File: 'NSDate+Formatting.m'
#import "NSDate+Formatting.h"
 
@implementation NSDate (Formatting)
 
- (NSString *)timeAgoInWords {
    // ...
}

@end

Usage:
NSDate* oldDate = [NSDate dateWithTimeIntervalSinceNow:180];
NSLog(@"Date was %@", oldDate.timeAgoInWords); // => 3 minutes ago
Ruby:
class String
  def blank?
    true
  end
end

"foo".blank? #=> true
Block

Basic

^{
    NSLog(@"This is a block");
}
Ruby:
lambda {
  puts "This is a lambda"
}
Declare a block variable simpleBlock accept no argument and return void:
void (^simpleBlock)(void);
Ruby:
foo = Proc.new {}
Assign a block to the variable:
simpleBlock = ^{
    NSLog(@"This is a block");
};
Ruby:
foo = Proc.new {
  puts "This is a proc"
}
Combine declaration and assignment:
void (^simpleBlock)(NSString *s) = ^{
    NSLog(@"This is a block");
};
Ruby:
foo = lambda { |a|
  puts "foobar - #{a}"
}
Blocks Can Capture Values from the Enclosing Scope

- (void)testMethod {
    int anInteger = 42;
 
    void (^testBlock)(void) = ^{
        NSLog(@"Integer is: %i", anInteger);
    };
    
    anInteger = 84;
 
    testBlock();
}
// => Integer is: 42
Ruby:

Use __block Variables to Share Storage

__block int anInteger = 42;

void (^testBlock)(void) = ^{
    NSLog(@"Integer is: %i", anInteger);
};

anInteger = 84;

testBlock();
// => Integer is: 84
Side effect:
Any Objective-C objects declared in this way will not be sent a -retain message. Another side-effect is that the variable will be shared by all blocks which access it, so modifications made by one block will be seen by another— they will not have their own mutable copies of the variable’s initial value.
Ruby:
a = 42
foo = lambda {
  puts "Integer is #{a}"
}
a = 64
foo.call()

#=> Integer is: 64
Nil

Every message send to nil will be IGNORED
Ruby:
NoMethodError: undefined method `a' for nil:NilClass
Ref:

http://www.slideshare.net/abdels/my-adventuresinobjc
http://blog.carbonfive.com/2012/01/23/monkey-patching-ios-with-objective-c-categories-part-1-simple-extensions-and-overrides/
http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html
http://blog.phusion.nl/2010/03/24/objective-c-for-ruby-developers-un-not-so-petit-interlude-1/
http://paulsturgess.co.uk/blog/2013/04/25/objective-c-for-a-rubyist/
https://speakerdeck.com/eddie/my-way-to-objective-c