Explain the concept of smart casts in Kotlin.

In Kotlin, smart casts are a feature that allows the compiler to automatically cast an object to a more specific type based on certain conditions. It is a mechanism that enhances type safety and reduces the need for explicit type checks and casts in your code. Here's how smart casts work and their benefits:

1. Type Checks :
   - Smart casts are triggered when you perform a type check using the `is` operator or use the `!is` operator for a negated type check.
   - When the compiler determines that a type check is true, it automatically casts the object to that specific type within the corresponding block of code.

2. Automatic Casting :
   * After a successful type check, the compiler treats the object as if it were of the checked type within the scope where the type check is performed.
   * This allows you to access properties and invoke functions specific to that type without the need for explicit casts.

3. Eliminates Explicit Casts :
   * Smart casts help eliminate the need for explicit casts (`as` operator) in your code, making it more concise and less error-prone.
   * The compiler tracks the type information and performs the necessary casts for you, reducing the risk of runtime ClassCastException errors.

4. Scoping :
   * Smart casts have scoping rules, meaning the casted object is available only within the scope where the type check is performed.
   * The object is casted to the more specific type within that scope, and outside that scope, it is treated as the original type. 5. Nullable Types :
   * Smart casts also work with nullable types (`T?`).
   * When you perform a null check (`!= null` or `== null`), the compiler smart casts the nullable type to a non-null type within the corresponding block of code.

Here's an example to illustrate the usage of smart casts :

fun processString(str: String?) {
    if (str != null) {
        // Compiler smart casts 'str' to non-null 'String' type
        println(str.length)
    }
}​

In the example, the smart cast is triggered after the null check (`str != null`). Within the block, the compiler automatically treats `str` as a non-null `String` type, allowing access to its `length` property without the need for an explicit cast.

Smart casts in Kotlin provide convenience and safety by reducing the verbosity of type checks and explicit casts. They improve code readability and make working with different types more intuitive, while also ensuring type safety at compile-time.