Weak typing
Encyclopedia
In computer science
, weak typing (a.k.a. loose typing) is a property attributed to the type system
s of some programming language
s. It is the opposite of strong typing, and consequently the term weak typing has as many different meanings as strong typing does.
One of the more common definitions states that weakly typed programming languages are those that support either implicit type conversion
(nearly all languages support at least one implicit type conversion), ad-hoc polymorphism (also known as overloading) or both. These less restrictive usage rules can give the impression that strict adherence to typing rules is less important than in strongly typed languages and hence that the type system is "weaker". However, such languages usually have restrictions on what programmers can do with value
s of a given type; thus it is possible for a weakly typed language to be type safe
. Moreover, weakly typed languages may be statically typed, in which case overloading is resolved statically and type conversion operations are inserted by the compiler, or dynamically typed, in which case everything is resolved at run time.
One claimed advantage of weak typing over strong typing is that it requires less effort on the part of the programmer because the compiler
or interpreter implicitly performs certain kinds of conversions. However, one claimed disadvantage is that weakly typed programming systems catch fewer errors at compile time and some of these might still remain after testing has been completed. Two commonly used languages that support many kinds of implicit conversion are C
and C++
, and it is sometimes claimed that these are weakly typed languages. However, others argue that these languages place enough restrictions on how operands of different types can be mixed, that the two should be regarded as strongly typed languages. PHP and Perl are two examples of weakly typed languages.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, weak typing (a.k.a. loose typing) is a property attributed to the type system
Type system
A type system associates a type with each computed value. By examining the flow of these values, a type system attempts to ensure or prove that no type errors can occur...
s of some programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
s. It is the opposite of strong typing, and consequently the term weak typing has as many different meanings as strong typing does.
One of the more common definitions states that weakly typed programming languages are those that support either implicit type conversion
Type conversion
In computer science, type conversion, typecasting, and coercion are different ways of, implicitly or explicitly, changing an entity of one data type into another. This is done to take advantage of certain features of type hierarchies or type representations...
(nearly all languages support at least one implicit type conversion), ad-hoc polymorphism (also known as overloading) or both. These less restrictive usage rules can give the impression that strict adherence to typing rules is less important than in strongly typed languages and hence that the type system is "weaker". However, such languages usually have restrictions on what programmers can do with value
Value (computer science)
In computer science, a value is an expression which cannot be evaluated any further . The members of a type are the values of that type. For example, the expression "1 + 2" is not a value as it can be reduced to the expression "3"...
s of a given type; thus it is possible for a weakly typed language to be type safe
Type safety
In computer science, type safety is the extent to which a programming language discourages or prevents type errors. A type error is erroneous or undesirable program behaviour caused by a discrepancy between differing data types...
. Moreover, weakly typed languages may be statically typed, in which case overloading is resolved statically and type conversion operations are inserted by the compiler, or dynamically typed, in which case everything is resolved at run time.
One claimed advantage of weak typing over strong typing is that it requires less effort on the part of the programmer because the compiler
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
or interpreter implicitly performs certain kinds of conversions. However, one claimed disadvantage is that weakly typed programming systems catch fewer errors at compile time and some of these might still remain after testing has been completed. Two commonly used languages that support many kinds of implicit conversion are C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
and C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
, and it is sometimes claimed that these are weakly typed languages. However, others argue that these languages place enough restrictions on how operands of different types can be mixed, that the two should be regarded as strongly typed languages. PHP and Perl are two examples of weakly typed languages.