Scala (programming language)
- This article is about the programming language. For other uses, see Scala.
Scala is a multi-paradigm programming language designed to express common programming patterns in a concise, elegant, and type-safe way. It smoothly integrates features of object-oriented and functional languages.
Scala is object-oriented
Scala is a pure object-oriented language in the sense that every value is an object. Types and behavior of objects are described by classes and traits. Class abstractions are extended by subclassing and a flexible mixin-based composition mechanism as a clean replacement for multiple inheritance.
Scala is functional
Scala is also a functional language in the sense that every function is a value. Scala provides a lightweight syntax for defining anonymous functions, it supports higher-order functions, it allows functions to be nested, and supports currying. Scala's case classes and its built-in support for pattern matching model algebraic types used in many functional programming languages.
Furthermore, Scala's notion of pattern matching naturally extends to the processing of XML data with the help of regular expression patterns. In this context, sequence comprehensions are useful for formulating queries. These features make Scala ideal for developing applications like web services.
Scala is statically typed
Scala is equipped with an expressive type system that enforces statically that abstractions are used in a safe and coherent manner. In particular, the type system supports:
- generic classes,
- variance annotations,
- upper and lower type bounds,
- classes and abstract types as object members,
- compound types,
- explicitly typed self references,
- views, and
- polymorphic methods.
Scala is extensible
The design of Scala acknowledges the fact that in practice, the development of domain-specific applications often requires domain-specific language extensions. Scala provides a unique combination of language mechanisms that make it easy to smoothly add new language constructs in form of libraries:
- any method may be used as an infix or postfix operator, and
- closures are constructed automatically depending on the expected type (target typing).
A joint use of both features facilitates the definition of new statements without extending the syntax and without using macro-like meta-programming facilities.
Scala interoperates with Java and .NET
Scala is designed to interoperate well with popular programming environments like the Java 2 Runtime Environment (JRE) and the .NET CLR. In particular, the interaction with mainstream object-oriented languages like Java and C# is as smooth as possible. Scala has the same compilation model (separate compilation, dynamic class loading) like Java and C# and allows access to thousands of high-quality libraries.
Hello World example
The Hello world program written in Scala:
object HelloWorld {
def main(args: Array[String]) = {
Console.println("Hello, world!");
}
}