What features and useful mnemonics of the Kotlin language do you know?

Kotlin has a number of features that make it a convenient and expressive language for development, especially on Android:

• Null Safety — built-in system to prevent NullPointerException using nullable and non-nullable types.
• Data classes — classes with automatic generation of equals(), hashCode(), toString(), and copy().
• Extension functions — ability to add new functions to existing classes without inheritance.
• Coroutines — lightweight threads for asynchronous programming.
• Smart casts — automatic type casting after checks.
• Type inference — the compiler infers variable types automatically.

Useful mnemonics and tricks:

• val — immutable variable (value), var — mutable (variable).
• fun — keyword for declaring a function.
• by lazy — lazy initialization.
• ?. — safe call operator.
• ?: — Elvis operator for default values.

Example of using safe call and Elvis operator:

val length = name?.length ?: 0 // returns length if name is not null, otherwise 0

These features make Kotlin code concise, safe, and readable.