Scala Reserved Words

Table lists the reserved keywords in Scala. Many are found in Java and they usually have the same meanings in both languages.

Word	Description
abstract	Makes a declaration abstract.
case	Start a case clause in a match expression. Define a “case class.”
catch	Start a clause for catching thrown exceptions.
class	Start a class declaration
def	Start a method declaration.
do	Start a do…while loop.
else	Start an else clause for an if clause.
extends	Indicates that the class or trait that follows is the parent type of the class or trait being declared.
false	Boolean false.
final	Applied to a class or trait to prohibit deriving child types from it. Applied to a member to prohibit overriding it in a derived class or trait.
finally	Start a clause that is executed after the corresponding try clause, whether or not an exception is thrown by the try clause.
for	Start a for comprehension (loop).
forSome	Used in existential type declarations to constrain the allowed concrete types that can be used.
if	Start an if clause.
implicit	Marks a method or value as eligible to be used as an implicit type converter or value. Marks a method parameter as optional, as long as a type-compatible substitute object is in the scope where the method is called.
import	Import one or more types or members of types into the current scope.
lazy	Defer evaluation of a val.
match	Start a pattern-matching clause.
new	Create a new instance of a class.
null	Value of a reference variable that has not been assigned a value.
object	Start a singleton declaration: a class with only one instance.
override	Override a concrete member of a type, as long as the original is not marked final.
package	Start a package scope declaration.
private	Restrict visibility of a declaration.
protected	Restrict visibility of a declaration.
requires	Deprecated. Was used for self-typing.
return	Return from a function.
sealed	Applied to a parent type. Requires all derived types to be declared in the same source file.
super	Analogous to this, but binds to the parent type.
this	How an object refers to itself. The method name for auxiliary constructors.
throw	Throw an exception.
trait	A mixin module that adds additional state and behavior to an instance of a class. Can also be used to just declare methods, but not define them, like a Java interface.
try	Start a block that may throw an exception.
true	Boolean true.
type	Start a type declaration.
val	Start a read-only “variable” declaration.
var	Start a read-write variable declaration.
while	Start a while loop.
with	Include the trait that follows in the class being declared or the object being instantiated.
yield	Return an element in a for comprehension that becomes part of a sequence.
_	A placeholder, used in imports, function literals, etc.
:	Separator between identifiers and type annotations.
=	Assignment.
=>	Used in function literals to separate the argument list from the function body.
<-	Used in for comprehensions in generator expressions.
<:	Used in parameterized and abstract type declarations to constrain the allowed types.
<%	Used in parameterized and abstract type “view bounds” declarations.
>:	Used in parameterized and abstract type declarations to constrain the allowed types.
#	Used in type projections.
@	Marks an annotation.
⇒	(Unicode \u21D2) Same as =>.
→	(Unicode \u2192) Same as ->.
←	(Unicode \u2190) Same as <-.

Note:
1. break and continue are not listed. These control keywords don’t exist in Scala.
2. Some Java methods use names that are reserved words by Scala, for example, java.util.Scanner.match. To avoid a compilation error, surround the name with single back quotes (“back ticks”), e.g., java.util.Scanner.`match`.

Ref

《Programming Scala》