Predeclared

In computer languages, the built-in information, encodings or tools that are available to a

, often in the form of entities, variables, objects, functions or instructions. It is mostly not possible to overwrite or otherwise manipulate them.

Pre-declared entity

A pre-declared entity is a built-in notation convention for a character or a string. For example, in the HTML markup language, a large number of character and numeric entities are available to represent characters. In HTML, '<' is a possible pre-declared entity to represent '<'. The programmer must not declare this entity by himself before he can use it, since it is already pre-declared by the specifications of the HTML language. Pre-declared entities are often used as escape sequences to represent information that would otherwise cause possible conflicts in its non-encoded form.

Pre-declared variable

When a variable is pre-declared, it provides the programmer with information that he might be interested in. For example, in the

variable %ENV is pre-declared, holding all kinds of environmental information such as the operating system

, host information, user information, and many more. Other pre-declared variables in Perl are %INC and %SIG. Almost all common programming languages provide the programmer with such pre-declared variables in one or another form.

When variables are pre-declared, it is commonly assumed that the value for the pre-declared name is also pre-assigned at the same time.

Pre-declared object

Pre-declared objects have the same goal as pre-declared variables. For example, in the JavaScript language, the navigator-object is available to get all kinds of information about the browser that is running the script in question.

Pre-declared functions and instructions

Pre-declared

modules

.

Narrow semantic sense

In a narrow strictly

variable before an assignment takes place. In the following example, the first line is the (pre-)declaration and the second the assignment

:

   var A;
   A = 1;

By declaring the name A, the program creates a namespace for the variable called A. In most modern languages, the variable does not need to be pre-declared on a separate line, as the following instruction achieves exactly the same:

   var A = 1;

In early computer languages, the variable always needed to be pre-declared as a separate instruction, because the

Declaration and assignment

are still two fundamental different things, though they nowadays mostly appear in a same instruction line.