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class C {
var x: C;
method M(S: set<C>, a: array<C>, b: array2<C>)
requires S != {};
modifies this, a, b;
{
x := new C;
x := new C.Init();
x := *;
x := choose S;
// test evaluation order
var c := x;
x := null;
x := new C.InitOther(x); // since the parameter is evaluated before the LHS is set, the precondition is met
assert x != c;
// test evaluation order and modification
if (*) {
var k := this.x;
var kx := this.x.x;
this.x.x := new C.InitAndMutate(this);
assert this.x == null;
assert this.x != k;
assert k.x != kx; // because it was set to a new object
assert fresh(k.x);
} else {
var k := this.x;
var kx := this.x.x;
this.x.x := new C.InitAndMutate(this);
var t := this.x.x; // error: null dereference (because InitAndMutate set this.x to null)
}
if (a != null && 10 <= a.Length) {
a[2] := new C;
a[3] := *;
}
if (b != null && 10 <= b.Length0 && 20 <= b.Length1) {
b[2,14] := new C;
b[3,11] := *;
}
}
method Init() { }
method InitOther(c: C)
requires c == null;
{
var d := new int[if c == null then 10 else -3]; // run-time error if c were non-null, but it ain't
}
method InitAndMutate(c: C)
requires c != null;
modifies c;
ensures c.x == null;
{
c.x := null;
}
}
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