# Section 8.10.1.1:
$IN_DEVICE

###### abstract class $IN_DEVICE

#### Formal Definitions

This abstract class defines a state component which is a set of all instantiations of objects of any class sub-typing from this class in addition to the vdm model types used wherever this class name is used. Note that SAME has to be an instantiated class, not an abstract one.

types
SAME = object_type ;
$IN_DEVICE = set of object_type
state
multi : $IN_DEVICE
inv multi_types ==
forall obj in set multi_types & sub_type($IN_DEVICE,obj)

NOTE | See the important note about vdm state in the notes on vdm-sl usage in this specification.

This abstraction models a device which, at least potentially, has the ability to obtain data from some device external to a program.

#### input_possible

This feature provides an enquiry facility for a program to determine whether input is currently possible from the instantiated class device.

input_possible | : BOOL

##### Formal Signature

input_possible(self : SAME) res : BOOL

##### Pre-condition

Since this feature is a predicate there is no pre-condition - ie it is vacuously true.

##### Post-condition

The result reflects the state of the real device being modelled by the instantiating class.

This predicate returns true if and only if the device is in a state where data can be imported by the program.

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