Introduction
Welcome to the tour
This tour contains bite-sized introductions to the most frequently used featuresof Scala. It is intended for newcomers to the language.
This is just a brief tour, not a full language tutorial. Ifyou want a more detailed guide, consider obtaininga book or takingan online courses.
What is Scala?
Scala is a modern multi-paradigm programming language designed to express common programming patterns in a concise, elegant, and type-safe way. It seamlessly integrates features of object-oriented and functional languages.
Scala is object-oriented
Scala is a pure object-oriented language in the sense thatevery value is an object. Types and behaviors of objects are described byclasses andtraits. Classes can be extended by subclassing, and by using a flexiblemixin-based composition mechanism as a clean replacement for multiple inheritance.
Scala is functional
Scala is also a functional language in the sense thatevery function is a value. Scala provides alightweight syntax for defining anonymous functions, supportshigher-order functions, allows functions to benested, and supportscurrying. Scala’scase classes and its built-in support forpattern matching provide the functionality of algebraic types, which are used in many functional languages.Singleton objects provide a convenient way to group functions that aren’t members of a class.
Scala is statically typed
Scala’s expressive type system enforces, at compile-time, that abstractions are used in a safe and coherent manner. In particular, the type system supports:
- Generic classes
- Variance annotations
- Upper andlower type bounds
- Inner classes andabstract type members as object members
- Compound types
- Explicitly typed self references
- Implicit parameters andconversions
- Polymorphic methods
Type inference means the user is not required to annotate code with redundant type information. In combination, these features provide a powerful basis for the safe reuse of programming abstractions and for the type-safe extension of software.
Scala is extensible
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 straightforward to add new language constructs in the form of libraries.
In many cases, this can be done without using meta-programming facilities such as macros. For example:
- Implicit classes allow adding extension methods to existing types.
- String interpolation is user-extensible with custom interpolators.
Scala interoperates
Scala is designed to interoperate well with the popular Java Runtime Environment (JRE). In particular, the interaction with the mainstream object-oriented Java programming language is as seamless as possible. Newer Java features like SAMs,lambdas,annotations, andgenerics have direct analogues in Scala.
Those Scala features without Java analogues, such asdefault andnamed parameters, compile as closely to Java as reasonably possible. Scala has the same compilation model (separate compilation, dynamic class loading) as Java and allows access to thousands of existing high-quality libraries.
Enjoy the tour!
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Contents
- Introduction
- Basics
- Unified Types
- Classes
- Default Parameter Values
- Named Arguments
- Traits
- Tuples
- Class Composition with Mixins
- Higher-order Functions
- Nested Methods
- Multiple Parameter Lists
- Case Classes
- Pattern Matching
- Singleton Objects
- Regular Expression Patterns
- Extractor Objects
- For Comprehensions
- Generic Classes
- Variances
- Upper Type Bounds
- Lower Type Bounds
- Inner Classes
- Abstract Type Members
- Intersection Types, aka Compound Types
- Self-type
- Contextual Parameters, aka Implicit Parameters
- Implicit Conversions
- Polymorphic Methods
- Type Inference
- Operators
- By-name Parameters
- Annotations
- Packages and Imports
- Top Level Definitions in Packages