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In computer science, an opaque data type is a data type whose concrete data structure is not defined in an interface. This enforces information hiding, since its values can only be manipulated by calling subroutines that have access to the missing information. The concrete representation of the type is hidden from its users, and the visible implementation is incomplete. A data type whose representation is visible is called transparent. [1] Opaque data types are frequently used to implement abstract data types.
Typical examples of opaque data types include handles for resources provided by an operating system to application software. For example, the POSIX standard for threads defines an application programming interface based on a number of opaque types that represent threads or synchronization primitives like mutexes or condition variables. [2]
An opaque pointer is a special case of an opaque data type, a datatype that is declared to be a pointer to a record or data structure of some unspecified data type. For example, the standard library that forms part of the specification of the C programming language provides functions for file input and output that return or take values of type "pointer to FILE
" that represent file streams (see C file input/output), but the concrete implementation of the type FILE
is not specified. [3]
Some languages, such as C, allow the declaration of opaque records (structs), whose size and fields are hidden from the client. The only thing that the client can do with an object of such a type is to take its memory address, to produce an opaque pointer.
If the information provided by the interface is sufficient to determine the type's size, then clients can declare variables, fields, and arrays of that type, assign their values, and possibly compare them for equality. This is usually the case for opaque pointers.
In some languages, such as Java, the only kind of opaque type provided is the opaque pointer. Indeed, in Java (and several other languages) records are always handled through pointers.
Some languages allow partially opaque types, e.g. a record which has some public fields, known and accessible to all clients, and some hidden fields which are not revealed in the interface. Such types play a fundamental role in object-oriented programming.
The information which is missing in the interface may be declared in its implementation, or in another "friends-only" interface. This second option allows the hidden information to be shared by two or more modules.
In computer science, an abstract data type (ADT) is a mathematical model for data types, defined by its behavior (semantics) from the point of view of a user of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations. This mathematical model contrasts with data structures, which are concrete representations of data, and are the point of view of an implementer, not a user. For example, a stack has push/pop operations that follow a Last-In-First-Out rule, and can be concretely implemented using either a list or an array. Another example is a set which stores values, without any particular order, and no repeated values. Values themselves are not retrieved from sets; rather, one tests a value for membership to obtain a Boolean "in" or "not in".
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A Berkeley (BSD) socket is an application programming interface (API) for Internet domain sockets and Unix domain sockets, used for inter-process communication (IPC). It is commonly implemented as a library of linkable modules. It originated with the 4.2BSD Unix operating system, which was released in 1983.
In software systems, encapsulation refers to the bundling of data with the mechanisms or methods that operate on the data. It may also refer to the limiting of direct access to some of that data, such as an object's components. Essentially, encapsulation prevents external code from being concerned with the internal workings of an object.
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Modula-3 is a programming language conceived as a successor to an upgraded version of Modula-2 known as Modula-2+. While it has been influential in research circles it has not been adopted widely in industry. It was designed by Luca Cardelli, James Donahue, Lucille Glassman, Mick Jordan, Bill Kalsow and Greg Nelson at the Digital Equipment Corporation (DEC) Systems Research Center (SRC) and the Olivetti Research Center (ORC) in the late 1980s.
The C standard library, sometimes referred to as libc, is the standard library for the C programming language, as specified in the ISO C standard. Starting from the original ANSI C standard, it was developed at the same time as the C library POSIX specification, which is a superset of it. Since ANSI C was adopted by the International Organization for Standardization, the C standard library is also called the ISO C library.
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In computer programming, an opaque pointer is a special case of an opaque data type, a data type declared to be a pointer to a record or data structure of some unspecified type.
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, dispose
, free
, release
depending on the language – which releases any resources the object is holding onto. Many programming languages offer language constructs to avoid having to call the dispose method explicitly in common situations.
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, but its proper name is Go.