Objective-C

Question 1

Tiobe

Answer 1

Code quality analysis company

Question 2

import

What kind of inclusion is this?

Answer 2

Textual inclusion. Fancy copy/paste with a few improvements over #include.

Question 3

What’s the problem?

#define readonly 1
#import

Answer 3

The macro defines readonly BEFORE the import, which means that definitions for readonly change within system files. This generates errors in the system files.

Question 4

import

What is the code size for

Answer 4

More than 350KB.

Question 5

What are the problems with precompiled headers?

Answer 5

UIKit/Cocoa framework used these. Creates namespace problems.

Question 6

What is

@import iAd;

Answer 6

Replaces #import . Imports framework semantics. No macro issues. No more “Choose Framework”. This is an opt-in build feature. Mapping of #import is automatic for legacy code.

Question 7

What is a workspace?

Answer 7

A group of projects.

Question 8

What is derived data?

Answer 8

Symbol indices, build products, window layouts, etc.

Question 9

When are modules supported?

Answer 9

iOS 7 & Mavericks. No C++ or user frameworks.

Question 10

What is (instancetype)?

Answer 10

It is a contextual keyword.

Question 11

What are explicitly-typed enums?

Answer 11

Enums that give errors when you assign to the wrong type.

Question 12

What are tagged pointers?

Answer 12

For small value-like objects, value is actually stored in the pointer. Bottom four bits are always zero because objects are 16-byte aligned. When that unused portion is 1, the rest of the pointer becomes data. Don’t exploit this! Implementation detail. :)

Question 13

What are boxed values?

Answer 13

Scalar values wrapped in objects.

Question 14

What is the convenience function equivalent of…

@’Z’

Answer 14

[NSNumber numberWithChar:’Z’]

Question 15

What is the difference between bool and BOOL?

Answer 15

bool is C, BOOL is Objective-C. YES and NO macros are defined as (BOOL)1 and (BOOL)0.

Question 16

What is this code:

@(getenv(“PATH”))

Answer 16

A boxed expression.

Question 17

How do you box an enum?

Answer 17

As a boxed expression:

enum foo {
FOO
}
@(FOO)

Question 18

What is CADisplayLink?

Answer 18

A Quartz Core Framework class that allows you to sync up drawing with the display rate.

Question 19

What is a blit?

Answer 19

Block Level Transfer.

Question 20

What is this?

^NSComparisonResult(id obj1, id obj2) { …

Answer 20

NSComparisonResult is the return type to denote the ordering of two objects. 
typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);