To better understand Arrays it is best to go back to the basics. The basics Suppose that we have to store data of 5 random samples of a product rating, in our normal way to do things we would probably go about by making 5 separate variables named rating1, rating2, rating3, etc. Swift 4 puts strict checking which does not allow you to enter a wrong type in an array, even by mistake. If you assign a created array to a variable, then it is always mutable, which means you can change it by adding, removing, or changing its items; but if you assign an array to a constant, then that array is immutable, and its size.
Apple describes
ArraySlice
as “Views onto Arrays”. It means that an ArraySlice
is an object which represents a subsequence of its array. It’s very powerful and allows us to perform the same array operations on a slice like append
, map
and so on.In this article, we will see how to create it and some internal behaviors to avoid troubles.
Happy Reading!
Before using an
ArraySlice
, we must understand how to create it. Swift provides several ways to get a slice from a given array:drop
Array provides some methods to create a subsequence removing some elements. These methods are
dropFirst
, dropLast
and drop
:prefix
If we want to create a subsequence with the first elements of a given array, we can use the method
prefix
:suffix
suffix
has the opposite behavior of prefix
. It returns the last elements of the array:Range
We can create an
ArraySlice
using also a range of indices: Iscreen recorder 3 8 0 8.With Swift 4, we can omit the
startIndex
if want to use the index 0 and the endIndex
if we want to use the last index of the array:Let’s suppose that we want to remove the last 5 elements from an array. We can use the method
dropLast(5)
and assign the result to the array:Unfortunately, Swift doesn’t allow to assign an
ArraySlice
object to an Array
. For this reason, in example above, we have a compile error Cannot assign value of type 'ArraySlice<Int>' to type '[Int]'
. We need a way to convert the ArraySlice
object to Array
. Fortunately, Swift allows us to cast the slice variable using the syntax Array(<slice_variable>)
. We can use this cast to fix the example above like this:Strong reference
ArraySlice
holds a strong reference of its array. It means that we should pay attention how we use the slice to avoid troubles with the memory. Apple added also a warning about it in the documentation: Long-term storage of ArraySlice instances is discouraged. A slice holds a reference to the entire storage of a larger array, not just to the portion it presents, even after the original array’s lifetime ends. Long-term storage of a slice may therefore prolong the lifetime of elements that are no longer otherwise accessible, which can appear to be memory and object leakage.
Macbooster 5 0 5. We can test this behavior with the following example:
If we let run this example, we can notice that the property
slice
holds a strong reference of the array elements. Even though arrayHandler
is destroyed at the end of the init
scope, the deinit
method of Element
is not called.Consequences of ArraySlice
and Array
changes
Let’s suppose that we have an
Array
and an its ArraySlice
. If we change the elements of the Array
, the ArraySlice
won’t be affected and will continue storing the original elements:Vice versa, if we change the elements of an
ArraySlice
, its Array
won’t be affected:ArraySlice
maintains the same indices of its array. It means that the element at index 3 of an ArraySlice
is the same element at the index 3 of its original array.Let’s consider an
ArraySlice
with a range 2..4
. If we try reading the element at index 0 of the slice, we would have a run time error:It happens because the slice doesn’t contain the element at index 0 of the array but only the elements at index 2, 3 and 4.
If we want to get the first and last index of a slice in a safe way, we should use
startIndex
and endIndex
:endIndex
returns the position one greater than the last valid index. For this reason, we must use endIndex - 1
in the example above to avoid an Index out of bounds
error.In addition to
ArraySlice
, Swift provides also a base object Slice. It allows us to get a subsequence of other collection objects like Dictionary
, Set
and any kind of custom collection.Contents
Welcome to Swift Tutorial. In this tutorial, we will learn about Swift String Arrays, how to create them, initialize and access them, etc. Short menu 2 3 download free.
Arrays are important derived datatypes in any functional programming language. Arrays help to store similar type of objects under a single variable name while providing access to the objects using an index.
String Arrays store multiple strings under a single variable name.
While getting started with String Arrays in Swift programming, let us see the syntax to create an empty array.
Create an empty String Array
To create an empty String Array, use the following syntax.
array_name
is used an identifier to access this String array.[Int]
specifies that this is an array which stores strings.There is no need to mention the size of an array while creation. The size of an empty String array is 0.
Create a String Array with a default value
Swift allows creating a String Array with a specific size and a default value for each string in the array.
To create a String Array with a specific size and default value, use the following syntax.
vararray_name= [String](repeating:default_value, count:array_size) |
where
array_size
is a number that defines the size of this array.default_value
is the default value for each string in this array.An example would be
varnames= [String](repeating:'tutorialkart', count:3) |
In the above statement, a String Array would be created with a size of 3 and a default value of “tutorialkart” for each item in the array.
Create a String Array with initial values
You can also create a String Array in Swift with initial values. Which means you can combine array declaration and initialization in a single statement.
![Array Array](https://petrofilm.com/yahoo_site_admin/assets/images/tyske_soldater_invaderer_Oslo.17260816_std.jpg)
varnames:[String] = ['TutorialKart','Swift Tutorial'] |
Note that there is a slight variation in the syntax. The
[String]
part comes to the left side.The initial values are enclosed in squared brackets and are separated by a comma.
Access String Array in Swift
Items of the String Array can be accessed using the index.
varnames:[String] = ['TutorialKart','Swift Tutorial', 'iOS Tutorial'] varname=names[1] print( 'String at index 1 is : (name)' ) |
Stringat index1is:Swift Tutorial |
Note: The index of an array starts at 0.
From the above example,
numbers[0] = 7
, numbers[1]=54
and so on.Swift 4 2d Array Example
Following are some the operations that can be performed on String Arrays in Swift.
Conclusion
Swift 4 2d Array C++
In this Swift Tutorial, we have learned to declare, initialize, access and other operations on String Arrays in Swift programming.