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// RUN: %dafny /compile:3 /print:"%t.print" /dprint:"%t.dprint" "%s" > "%t"
// RUN: %diff "%s.expect" "%t"
trait Automobile {
ghost var Repr: set<object>
predicate Valid()
reads this //, Repr
ensures Valid() ==> this in Repr
function method Brand(): string
var position: int
method Drive()
requires Valid()
modifies this // Repr
ensures old(position) <= position
}
class Volvo extends Automobile {
predicate Valid()
reads this //, Repr
ensures Valid() ==> this in Repr
{
this in Repr
}
constructor()
modifies this
ensures Valid()
{
Repr := {this};
}
function method Brand(): string {
"Volvo"
}
method Drive()
// requires Valid()
modifies this // Repr
ensures old(position) <= position
{
position := position + 10;
}
}
class Fiat extends Automobile {
predicate Valid()
reads this // , Repr
ensures Valid() ==> this in Repr
{
this in Repr
}
constructor()
modifies this
ensures Valid()
{
Repr := {this};
}
function method Brand(): string {
"Fiat"
}
method Drive()
// requires Valid()
modifies this // Repr
ensures old(position) <= position
{
position := position + 3;
}
}
method Main() {
var auto: Automobile;
auto := new Volvo();
WorkIt(auto);
auto := new Fiat();
WorkIt(auto);
}
method WorkIt(auto: Automobile)
requires auto != null && auto.Valid()
modifies auto // auto.Repr
{
auto.Drive();
print auto.Brand(), ": ", auto.position, "\n";
auto.position := 0;
}
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