- 01Setting up (what you'll need)
- 02Your first output (NSLog)
- 03Using variables
- 04Branching (the if statement)
- 05Repeating (the for loop)
- 06Writing your own function
- 07Working with arrays
- 08Repeating (the while loop)
- 09Working with classes (object orientation)
- 10Error handling (@try / @catch)
- 11Sorting an array
- 12Recursive functions
- 13The string standard library
- 14The switch statement
- 15The ternary operator
- 16Extending a class with a category
- 17Writing comments
- 18Logical operators (&&, ||, !)
- 19Constants (static const)
- 20Splitting and joining strings
- 21Writing nil-safe code
- 22Searching an array (containsObject:)
- 23Transforming an array (the map equivalent)
- 24Two-dimensional arrays (tabular data)
- 25Custom errors (categorising with NSError)
- 26Writing a variadic function
- 27Handling sets (data without duplicates) with NSSet
- 28Checking correctness (a first step towards testing)
- 29Higher-order functions (passing a block as an argument)
- 30Stacks and queues (the basics of data structures)
- 31The basics of type conversion (casting)
- 32An introduction to regular expressions (pattern matching)
- 33The binary search algorithm
- 34Building a Caesar cipher (a letter-shifting cipher)
- 35Understanding how bubble sort works
- 36Assembling and displaying a date (NSDateComponents)
- 37Writing several tests together (multiple test cases)
- 38Speeding up calculation with memoization (caching)
- 39Normalizing strings (trimming whitespace, unifying case)
- 40Shallow copies versus deep copies
- 41The basics of enums
- 42Flattening an array
- 43Reversing a string and testing for a palindrome
- 44Pairing up two arrays (the zip operation)
- 45Rounding numbers (floor, ceil, round)
- 46Multi-line text (joining adjacent string literals)
- 47Returning several values from a function (NSDictionary)
- 48Finding the GCD and LCM (the Euclidean algorithm)
- 49Formatting numbers (aligning digits and decimal places)
- 50Cleaning up with @try / @catch / @finally
- 51Type-agnostic general functions (the id type)
- 52The basics of reading and writing files
- 53Generating random numbers
- 54Bitwise operations (AND, OR, XOR, shifts)
- 55Receiving command-line arguments
- 56Pausing for a set time ([NSThread sleepForTimeInterval:])
- 57Watch out for floating-point error
- 58Reading a value from standard input
- 59FizzBuzz (the classic exercise)
- 60Testing whether a number is prime
- 61Set operations with NSSet (union, intersection, difference)
- 62Converting between bases (binary and hexadecimal)
- 63Checking that brackets match (an application of stacks)
- 64Testing whether two words are anagrams
- 65Testing whether a year is a leap year
- 66Converting temperatures (Celsius and Fahrenheit)
- 67Finding the prime factors
- 68[Project] Build a simple grade-tallying program
Shallow copies versus deep copies
This lesson covers the difference between shallow and deep copies in Objective-C, with the aim of avoiding bugs caused by unintentionally shared data.
Assigning an Objective-C object to another variable in fact copies a reference pointing at the same thing. That is a shallow copy, and changing one affects the other.
In the sample code, NSMutableDictionary *shallow = original; makes shallow point at the same dictionary instance as original. Changing it with shallow[@"city"] = @"Osaka" therefore changes what original[@"city"] displays too.
A common early stumble is the bug where "I copied it, but the original changed as well". When you want an independent copy you have to call mutableCopy or copy explicitly.
In professional work, understanding how reference types behave is unavoidable knowledge for handling Objective-C's memory correctly.
๐งช This site can't compile or run Objective-C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser โ nothing is sent anywhere).