- Contents
- Scope
- Context
- Class
- Scope of interest
Scopes
A scope describes the reach of a particular set of variables, functions, and other name-mapped data.
In Ferret, each scope has an associated scope object, the properties of which are lexical variables. Inheritance of lexical variables from outer scopes is possible through the same ISA inheritance system used for all objects.
Scope
Scope is the base type of all scopes. The current scope object is always
accessible by the special variable *scope.
Context
Context is a subtype of Scope which represents a namespace. The current
context is determined by a package declaration. If no
package is declared, package main is inferred.
At document level, the scope is not the current context itself but rather a
private file scope which inherits from it. This makes it possible to confine
variables to the current file rather than exposing them globally. To share
variables between files and packages, a share variable
declaration is needed.
For many document-level constructs, the data are assigned to a property of the
current context (and are therefore global) rather than the private file scope,
unless the construct name starts with an underscore (_), indicating that it is
private to the file scope. See scopes of interest for more
information on private scopes.
Class
Class is not technically a subtype of Scope. Within a
class definition, the scope is actually a private class
scope which inherits from both the class itself and the outer
context.
This means that lexical variables defined at class level are only accessible
from within the class definition unless they are explicitly exported with a
share variable declaration. In this case, they become
properties of the class.
Other constructs at class level such as functions, methods, and type definitions are exported by default; see scopes of interest for more info on that.
Scope of interest
Many constructs refer to a "scope of interest" (SOI), which determines the external availability of the data associated with the construct.
At document or package level, the SOI is the current context (as determined
by a package declaration), unless the construct name
starts with an underscore (_), in which case it is the private file scope. The
associated data (if public) will be accessible as a property of the context.
At class level, the SOI is the class itself, unless the construct name
starts with an underscore (_), in which case it is the private class scope.
The associated data (if public) will be accessible as a property of the class.
At any other level, the SOI is the current scope, and the underscore has no special meaning.