Keywords and Operators

• • is used for type casts
  • specifies an
• as? is used for safe type casts
• break
• class declares a class
• continue
• do begins a do/while loop (loop with postcondition)
• else defines the branch of an which is executed when the condition is false
• false specifies the ‘false’ value of the Boolean type
• for begins a
• fun declares a function
• if begins an
• in
  • specifies the object being iterated in a for loop
  • is used as an infix operator to check that a value belongs to , a collection or another entity that defines the ‘contains’ method
  • is used in for the same purpose
  • marks a type parameter as contravariant
• !in
  • is used as an operator to check that a value does NOT belong to , a collection or another entity that defines the ‘contains’ method
  • is used in for the same purpose
• interface declares an interface
• is
  • checks that
  • is used in when expressions for the same purpose
• !is
  • checks that
  • is used in when expressions for the same purpose
• null is a constant representing an object reference that doesn’t point to any object
• object declares
• package specifies the package for the current file
• return
• super
  • refers to the superclass implementation of a method or property
• this
  • refers to the current receiver
• throw throws an exception
• true specifies the ‘true’ value of the
• try begins an exception handling block
• typeof reserved for future use
• val declares a read-only or local variable
• var declares a mutable or local variable
• when begins a (executes one of the given branches)
• while begins a while loop (loop with precondition)

• by
  • delegates the implementation of accessors for a property to another object
• catch begins a block that
• constructor declares a primary or secondary constructor
• delegate is used as an
• dynamic references a dynamic type in Kotlin/JS code
• field is used as an
• file is used as an annotation use-site target
• finally begins a block that
• get
  • declares the getter of a property
  • is used as an
• imports a declaration from another package into the current file
• init begins an
• param is used as an annotation use-site target
• property is used as an
• receiveris used as an annotation use-site target
• set
  • declares the
  • is used as an annotation use-site target
• setparam is used as an
• where specifies constraints for a generic type parameter

• actual denotes a platform-specific implementation in
• abstract marks a class or member as abstract
• annotation declares an
• companion declares a companion object
• const marks a property as a
• crossinline forbids non-local returns in a lambda passed to an inline function
• data instructs the compiler to
• enum declares an enumeration
• expect marks a declaration as , expecting an implementation in platform modules.
• external marks a declaration as implemented not in Kotlin (accessible through JNI or in )
• final forbids overriding a member
• infix allows calling a function in
• inline tells the compiler to inline the function and the lambdas passed to it at the call site
• inner allows referring to the outer class instance from a
• internal marks a declaration as visible in the current module
• lateinit allows initializing a
• noinline turns off inlining of a lambda passed to an inline function
• open allows
• out marks a type parameter as covariant
• override marks a member as an
• private marks a declaration as visible in the current class or file
• protected marks a declaration as
• public marks a declaration as visible anywhere
• reified marks a type parameter of an inline function as
• sealed declares a sealed class (a class with restricted subclassing)
• suspend marks a function or lambda as suspending (usable as a )
• tailrec marks a function as tail-recursive (allowing the compiler to replace recursion with iteration)
• vararg allows

• field is used inside a property accessor to refer to the backing field of the property
• it is used inside a lambda to

• +, , *, /, % - mathematical operators
  • * is also used to pass an array to a vararg parameter
• =
  • assignment operator
  • is used to specify
• +=, -=, *=, /=, %= - augmented assignment operators
• ++, -- -
• &&, ||, ! - logical ‘and’, ‘or’, ‘not’ operators (for bitwise operations, use corresponding infix functions)
• ==, != - (translated to calls of equals() for non-primitive types)
• ===, !== - referential equality operators
• <, >, <=, >= - (translated to calls of compareTo() for non-primitive types)
• [, ] - indexed access operator (translated to calls of get and set)
• !!
• ?. performs a safe call (calls a method or accesses a property if the receiver is non-null)
• ?: takes the right-hand value if the left-hand value is null (the )
• :: creates a member reference or a
• .. creates a range
• : separates a name from a type in declarations
• ? marks a type as
• ->
  • separates the parameters and body of a lambda expression
  • separates the parameters and return type declaration in a
  • separates the condition and body of a when expression branch
• @
  • introduces an
  • introduces or references a loop label
  • introduces or references a
  • references a ‘this’ expression from an outer scope
  • references an
• ; separates multiple statements on the same line
• references a variable or expression in a string template
• _
  • substitutes an unused parameter in a
  • substitutes an unused parameter in a destructuring declaration