[P] Programming

move_to_right
.x = r(x)
.y = r(y)
class — Class programming 29
and program move to right.ado had lines in it referring to .x and .y, they would be interpreted
as .impliedcontext.x and .impliedcontext.y.
In all programs—member programs or ado-files—we can explicitly control whether we want
identifiers in the implied context or globally with the .Local and .Global prefixes; see 9. Prefix
operators.
3. Version control
The first thing that should appear in a .class file is a version statement; see [P] version. For
example, coordinate.class reads
begin coordinate.class
version 11
[ class statement defining member variables omitted ]
program .set
args x y
.x = ‘x’
.y = ‘y’
end
end coordinate.class
The version 11 at the top of the file specifies not only that, when the class definition is read,
it be interpreted according to version 11 syntax, but also that when each of the member programs
runs, it be interpreted according to version 11. Thus you do not need to include a version statement
inside the definition of each member program, although you may if you want that one program to
run according to the syntax of a different version of Stata.
Including the version statement at the top, however, is of vital importance. Stata is under continual
development, and so is the class subsystem. Syntax and features can change. Including the version
command ensures that your class will continue to work as you intended.
4. Member variables
4.1 Types
The second thing that appears in a .class file is the definition of the member variables. We have
seen two examples:
begin coordinate.class
and
version 11
class coordinate {
double x
double y
}
[ member programs omitted ]
end coordinate.class