Basic Operator, String and Characters in Swift.

Swift Study Group
Basic Operator, String
and Characters
2015/8/11
Joe

Outline
• Basic Operators
• Strings and Characters

Kind of Operators
• Unary: -a, !b, i++
• Binary: 2+3
• Ternary: a ? b : c

Assignment Operator
• let a = 1
• let (a,b) = (1,2)
• if x = y { } : the behavior of assigning value will
not return value

Arithmetic Operators
• +: It is also supported for String concatenation.
• %: It is also operate on ﬂoating-point numbers
• Question:
• -8 % 3
• 5 / -2
• 8 % 2.5

Increment and Decrement
Operators
• If the operator is written before the variable, it
increments the variable before returning its
value.
• ++i
• If the operator is written after the variable, it
increments the variable after returning its value.
• i++

Increment and Decrement
Operators
var i = 1
i++
i
i = 1
++i
i

Others
• Unary Minus Operator: -3
• Unary Plus Operator: +3
• Compound Assignment Operators: a += 2
• Ternary conditional operator: hasHeader ? 2 : 3
• Logical Operator: NOT(!), AND(&&), OR(||)

Comparison Operators
• a === b
• a != b
• a > b
• a < b
• a >= b
• a <= b
• a === b
let a = NSObject()
let b = NSObject()
let c = a
a === b
a === c
How about string comparison ?

Nil Coalescing Operator
• The nil coalescing operator (a ?? b) unwraps an
optional if it contains a value, or returns a default
value b if a is nil.
• (a != nil) ? a! : b

Range Operators
• Closed Range Operator: 1…5
• Half-Open Range Operator: 1..<5

Composition of String
• String -> Character -> extended grapheme
cluster -> Unicode scalar

String
• Literal: “ ”
• Empty String: a = “”, a = String(), a.isEmpty
• Mutability: var s = “Hello” s+=“World”
• Strings are value types not reference types.
• Concatenating with Character:  
let exclamationMark: Character = “!” 
s += exclamationMark

Characters
• String type represents a collection of Character
value in a speciﬁed order.
• String value can be constructed by passing an
array of Character values as an argument to its
initializer

String Interpolation
• String interpolation is a way to construct a new
String value from a mix of constants, variables,
literals and expressions by including their values
inside a string literal.
• let multiplier = 3 
let message = “(multiplier) times 2.5 is
(Double(multiplier) * 2.5)”

Unicode
• Unicode is an international standard for
encoding, representing, and processing text in
different writing systems.

Unicode Scalars
• A Unicode scalar is a unique 21-bit number for
character or modiﬁer, such as U+0061 for “a” 
U+1F425 for

Special Character in String
Literal (1/2)
• Special Characters
• 0 null character
• backslash
• t horizontal tab
• n line feed
• r carriage return
• ” double quote
• ’ single quote
let message = ""Hello World""

Special Character in String
Literal (2/2)
• An arbitrary Unicode scalar, written as u{n},
where n is 1-8 digit hexadecimal number with a
value equal to a valid Unicode code point.
var str = "u{1F425}"

Extended Grapheme
Clusters(1/2)
• Every instance of Swift’s Character type
represents a single extended grapheme cluster.
• An extended grapheme cluster is a sequence of
one or more Unicode scalars that produce a
single human-readable character.

Extended Grapheme
Clusters(2/2)
is composed of one or two Unicode Scalars
which is a single extended grapheme cluster
is composed of one or three Unicode Scalars
which is a single extended grapheme cluster

Counting Characters
var word = "cafe"
count(word)
word += "u{301}"
count(word)

Accessing and Modifying a
String
• Swift strings cannot be indexed by integer
values.
• Using String index instead.Type: String.Index

String.Index
• startIndex
• endIndex
• startIndex.successor()
• endIndex.predecessor()
• indices

Inserting and Removing
• insert(_:atIndex) : To insert a character into a
string at a specified index.
• splice(_:atIndex) : To insert another string at a
specified index.
• removeAtIndex(_:atIndex): To remove a character
from a string at a specified index.
• removeRange(_:range): To remove a substring at
a specified range.

String and Character
Equality
• ==, !=
• Two string values are considered equal if their
extended grapheme clusters are canonically
equivalent if they have the same linguistic
meaning and appearance.

Prefix and Suffix Equality
• hasPrefix(_:)
• hasSuffix(_:)

Unicode Representation of
Strings
• When a Unicode string is written to a text ﬁle or
some other storage, the Unicode scalars in that
string are encoded in one of several Unicode-
deﬁned encoding forms.
• UTF-8
• UTF-16
• Unicode Scalar

Reference
• The Swift Programming Language
• https://gist.github.com/joehsieh/
5dffe9a5e49421c8cde5

Basic Operator, String and Characters in Swift.

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