This article is about type systems in computer programming. For the formal study of type systems, see Type theory.
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Type systems
General concepts
Type safety
Strong vs. weak typing
Major categories
Static vs. dynamic
Manifest vs. inferred
Nominal vs. structural
Duck typing
Minor categories
Abstract
Dependent
Flow-sensitive
Gradual
Intersection
Latent
Refinement
Substructural
Unique
Session
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In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type (for example, integer, floating point, string) to every term (a word, phrase, or other set of symbols). Usually the terms are various language constructs of a computer program, such as variables, expressions, functions, or modules.[1] A type system dictates the operations that can be performed on a term. For variables, the type system determines the allowed values of that term. Type systems formalize and enforce the otherwise implicit categories the programmer uses for algebraic data types, data structures, or other components (e.g. "string", "array of float", "function returning boolean").
Type systems are often specified as part of programming languages and built into interpreters and compilers, although the type system of a language can be extended by optional tools that perform added checks using the language's original type syntax and grammar. The main purpose of a type system in a programming language is to reduce possibilities for bugs in computer programs due to type errors.[2] The given type system in question determines what constitutes a type error, but in general, the aim is to prevent operations expecting a certain kind of value from being used with values of which that operation does not make sense (validity errors). Type systems allow defining interfaces between different parts of a computer program, and then checking that the parts have been connected in a consistent way. This checking can happen statically (at compile time), dynamically (at run time), or as a combination of both. Type systems have other purposes as well, such as expressing business rules, enabling certain compiler optimizations, allowing for multiple dispatch, and providing a form of documentation.
^Pierce 2002, p. 1: "A type system is a tractable syntactic method for proving the absence of certain program behaviors by classifying phrases according to the kinds of values they compute."
^Cardelli 2004, p. 1: "The fundamental purpose of a type system is to prevent the occurrence of execution errors during the running of a program."
In computer programming, a typesystem is a logical system comprising a set of rules that assigns a property called a type (for example, integer, floating...
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prevents type errors. Typesystem, defines a programming language's response to data types. Type (model theory) Type theory, basis for the study of type systems...
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under static enforcement. In the context of static (compile-time) typesystems, type safety usually involves (among other things) a guarantee that the...
dependent type is a type whose definition depends on a value. It is an overlapping feature of type theory and typesystems. In intuitionistic type theory...
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defined by a formal language. Languages usually provide features such as a typesystem, variables and mechanisms for error handling. An implementation of a...
component system. This is consistent with a traditional use of system term in general systems engineering with Common Lisp Object System and typesystem as examples...
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