SIMSCRIPT II.5 Programming Language

Advanced Topics
6.5 Attribute Definitions: Functions
When defined by statements of the form:
the system has an attribute name function
every entity name has an attribute name function
a system attribute or an attribute of a permanent or temporary entity is treated as a function and not
as a variable. Any reference to such a function attribute is in effect a reference to a function routine
with the same name. That is, a subprogram having the same name as the declared attribute must be
included as one of the program routines. The routine must have the same number of arguments as
the declared or implied dimensionality of the attribute, that is, no arguments for an unsubscripted
system attribute, one argument for a temporary or permanent entity, two arguments for a two-dimensional
system attribute, etc.
Function attributes, because they are computational procedures, have no storage space allocated to
them. Declarations of attributes as functions interspersed between other attribute declarations have
no effect, therefore, on storage allocation of attributes to arrays or entity records. To illustrate:
Declaration:
every AUTO has a FUEL FUNCTION, a CONSUMPTION.RATE,
a FUEL.CAPACITY and a DEPARTURE.TIME
Entity structure:
word 1
word 2
word 3
CONSUMPTION.RATE
FUEL.CAPACITY
DEPARTURE.TIME
Assume the function attribute, FUEL, is defined by the following routine:
routine FUEL(AUTO)
return with FUEL.CAPACITY(AUTO) -
(TIME - DEPARTURE.TIME(AUTO)) *
CONSUMPTION.RATE(AUTO)
end
Assuming that the value of the current time is maintained in a global variable, TIME, the amount of
fuel currently remaining in a particular auto is calculated at each apparent attribute reference of the
type:
let AMOUNT = FUEL(AUTO)
As the variable TIME changes, the reported value of FUEL(AUTO) changes.
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