📝 String Templates

1. Simple template - $variable

val name = "Alice"
val age = 25

println("Hello, $name!")           // Hello, Alice!
println("I am $age years old")     // I am 25 years old

2. Expression template - ${expression}

val a = 10
val b = 20

println("Sum: ${a + b}")           // Sum: 30
println("Max: ${if (a > b) a else b}")  // Max: 20

3. Template với properties

data class Person(val name: String, val age: Int)

val person = Person("Bob", 30)
println("${person.name} is ${person.age} years old")

4. Template với function calls

fun square(x: Int) = x * x

val num = 5
println("Square of $num is ${square(num)}")  // Square of 5 is 25

5. Escape $ symbol

val price = 100
println("Price: \$${price}")  // Price: $100

// Hoặc dùng raw string
println("""Price: ${'$'}$price""")

6. Multi-line templates

val name = "Alice"
val items = listOf("Apple", "Banana", "Orange")

val message = """
    Hello, $name!
    You have ${items.size} items:
    ${items.joinToString(", ")}
""".trimIndent()

println(message)

7. Template với nullable

val name: String? = null

println("Name: ${name ?: "Unknown"}")  // Name: Unknown
println("Length: ${name?.length ?: 0}")  // Length: 0

8. Complex expressions

val numbers = listOf(1, 2, 3, 4, 5)

println("Even numbers: ${numbers.filter { it % 2 == 0 }}")
println("Sum: ${numbers.sum()}")
println("Average: ${numbers.average()}")

9. Ví dụ thực tế: Format output

data class Product(val name: String, val price: Double, val quantity: Int)

val products = listOf(
    Product("Laptop", 15000000.0, 2),
    Product("Mouse", 200000.0, 5)
)

for (product in products) {
    println("""
        Product: ${product.name}
        Price: ${"%,.0f".format(product.price)} VNĐ
        Quantity: ${product.quantity}
        Total: ${"%,.0f".format(product.price * product.quantity)} VNĐ
    """.trimIndent())
}

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📝 Tóm tắt

• $variable - Simple variable interpolation
• $\{expression\} - Expression interpolation
• \$ - Escape dollar sign
• Có thể gọi functions, properties, expressions
• Hoạt động với cả regular và raw strings
• Kết hợp tốt với null safety operators