Is nil true in Objective-C?

In Objective-C, nil is defined as a value called __DARWIN_NULL , which essentially evaluates to 0 or false in if-statements. Therefore, writing if (x == nil) is the same as writing if (!

How to check nil in Objective-C?

length == 0) . object. length will return 0 if object == nil , so this test covers nil objects and strings with length 0. If you treat a string of length 0 different from a nil string, just check if object == nil .

Can bool be nil?

You can’t. A BOOL is either YES or NO . There is no other state. The way around this would be to use an NSNumber ( [NSNumber numberWithBool:YES]; ), and then check to see if the NSNumber itself is nil .

What is object in Objective-C?

In object-oriented programming terms, an object is an instance of a class. This chapter demonstrates how to define classes in Objective-C by declaring an interface, which describes the way you intend the class and its instances to be used.

Is Boolean yes or no?

By convention, we use the BOOL type for Boolean parameters, properties, and instance variables and use YES and NO when representing literal Boolean values. Because NULL and nil zero values, they evaluate to “false” in conditional expressions.

What is a bool true?

In computer science, a boolean data type is any data type of true or false value, yes or no value, or on or off (1 or 0) value. By default, the boolean data type is set to false.

What does nil mean C?

Objective-C builds on C’s representation of nothing by adding nil . nil is an object pointer to nothing. Although semantically distinct from NULL , they are technically equivalent.

What is an ID in Objective-C?

id is a data type of object identifiers in Objective-C, which can be use for an object of any type no matter what class does it have. id is the final super type of all objects.

How do I check Boolean value?

A Boolean value is one with two choices: true or false, yes or no, 1 or 0. In Java, there is a variable type for Boolean values: boolean user = true; So instead of typing int or double or string, you just type boolean (with a lower case “b”).

How do you know if boolean is optional?

Optionals no longer implicitly evaluate to true when they have a value and false when they do not, to avoid confusion when working with optional Bool values. Instead, make an explicit check against nil with the == or != operators to find out if an optional contains a value.

Is Swift or Objective-C better?

Apple claims Swift to be 2.6 times faster than Objective-C. To optimize memory management Swift employs ARC (Automatic Reference Counting). Moreover, Swift supports Dynamic libraries which boost application performance as well. Swift wins, and its advantage over Objective-C will grow.

What does super mean in Objective-C?

There’s another important keyword available to you in Objective-C, called super . Sending a message to super is a way to call through to a method implementation defined by a superclass further up the inheritance chain. The most common use of super is when overriding a method.

When to use nil begets nil in Objective C?

But in Objective-C, invoking a method on nil returns a zero value — which is to say, “nil begets nil“ . This fact alone significantly simplifies things for Objective-C developers, as it obviates the need to check for nil before doing anything:

When to use null vs nil in Cocoa?

Use NULL for non-object pointers. Context is a void * (ie a C-style pointer), so you’d definitely use NULL (which is sometimes declared as (void *)0) rather than nil (which is of type id ).

What’s the difference between a null and a nil?

NULL is for void * and nil is for id. Therefore, you pass NULL. If you pass nil, you are lying to your reader, who will think this method takes an id. – Peter Hosey Feb 17 ’09 at 18:50 Or to think of it another way, NULL is a broader type, and nil is a subset of NULL.

What’s the difference between nsnull and nil in Foundation?

On the framework level, Foundation defines NSNull, which defines a class method, +null, which returns the singleton NSNull object. NSNull is different from nil or NULL, in that it is an actual object, rather than a zero value. Additionally, in Foundation/NSObjCRuntime.h, Nil is defined as a class pointer to nothing.