String.count / isEmpty / String Literals

// Declaring strings
let str = "text"
var mutable = "mutable string"

// String interpolation
let message = "The value is \(variable)"

// Multi-line string literal
let multiline = """
    Line 1
    Line 2
    Line 3
    """

// Get character count
str.count

// Check if empty
str.isEmpty

// String basics
let greeting = "Hello"
print(greeting.count)    // 5
print(greeting.isEmpty)  // false

let empty = ""
print(empty.isEmpty)     // true

// String interpolation
let name = "Taro"
let age = 25
let intro = "\(name) is \(age) years old. Next year they will be \(age + 1)."
print(intro)

// Multi-line string literal
let poem = """
    Spring is the dawn,
    Summer is the night,
    Autumn is the dusk,
    Winter is the early morning.
    """
print(poem)

// String concatenation
var message = "Hello"
message += ", World"
message = message + "!"
print(message)  // Hello, World!

// Unicode and character count difference
let emoji = "👨‍👩‍👧‍👦"  // Family emoji (counts as 1 character)
print(emoji.count)         // 1
print(emoji.utf8.count)    // Byte count (emoji uses multiple bytes)

// Practical character count validation
func validateUsername(_ username: String) -> Bool {
    return !username.isEmpty && username.count <= 20
}
print(validateUsername("Taro"))  // true
print(validateUsername(""))      // false

Swift's String.count counts characters in units of Unicode extended grapheme clusters. This means emoji (👨‍👩‍👧‍👦) and combining characters (é = e + ´) each count as a single character.

isEmpty is more efficient than checking count == 0. Use utf8.count when you need the byte count, and unicodeScalars.count when you need the Unicode scalar count. For multilingual apps, it is recommended to always use count (grapheme clusters).

For string searching and matching, see String.hasPrefix() / hasSuffix() / contains().