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class MyClass {
var x: int;
var y: int;
ghost var g: int;
method M(S: set<MyClass>, mc: MyClass)
requires this == mc;
modifies this, S;
{
if mc == this {
modify mc, this;
}
modify {this}, this, {this}, S;
modify this;
modify {:myAttribute} {:another true} {this}, this, S;
modify ;
}
method N()
modifies this;
{
x := 18;
modify this;
assert x == 18; // error: cannot conclude this here
}
method P(other: MyClass)
modifies this;
{
x := 18;
var previous := if other == null then 0 else other.x;
modify this;
assert other != null && other != this ==> other.x == previous;
}
method FieldSpecific0()
modifies `x;
{
modify this; // error: this is a larger frame than what FieldSpecific0 is allowed to modify
}
method FieldSpecific1()
modifies `x, `y;
{
modify this; // error: this is a larger frame than what FieldSpecific0 is allowed to modify
}
method FieldSpecific2()
modifies this;
{
modify `x;
}
method FieldSpecific3()
modifies `x;
{
modify this`x;
modify `y; // error: this is a larger frame than what FieldSpecific3 is allowed to modify
}
method FieldSpecific4()
modifies `x;
{
var xx, yy := x, y;
modify this`x;
assert y == yy; // fine
assert x == xx; // error: x just changed
}
ghost method GhostFrame0()
modifies `x, `g; // the `x has no effect, since this is a ghost context
{
modify `x, `g;
}
ghost method GhostFrame1()
modifies `g;
{
modify `x, `g; // the `x has no effect, since this is a ghost context
}
ghost method GhostFrame2()
{
var xx := x;
modify `x; // fine, since we're in a ghost context, so `x doesn't count
assert xx == x; // fine
}
method GhostFrame3()
{
var xx := x;
if g < 100 {
// we're now in a ghost context
modify `x; // fine, since `x doesn't count here
}
assert xx == x; // fine
}
method GhostFrame4()
modifies this;
{
var xx := x;
ghost var gg := g;
if g < 100 {
// we're now in a ghost context
var n := 0;
while n < y
modifies `x;
{
if * {
g := g + 1; // error: this is an error here, since it violates the loop's modifies clause
}
n := n + 1;
}
n := 0;
while n < y
modifies `x, `g;
{
g := g + 1;
n := n + 1;
}
}
assert x == xx; // fine, since only ghost state is allowed to be modified inside the ghost if
assert g == gg; // error
}
ghost method Ghost0()
modifies this;
{
var xx := x;
var gg := g;
modify this; // since we're in the context of a ghost method, this will only modify ghost fields
assert x == xx; // fine
assert g == gg; // error
}
ghost method Ghost1()
modifies this;
{
var xx := x;
var gg := g;
modify `x, `g; // since we're in the context of a ghost method, this will only modify
// ghost fields, despite the specific mention of non-ghost fields
assert x == xx; // fine
assert g == gg; // error
}
method Ghost2()
modifies this;
{
var xx := x;
ghost var gg := g;
if g < 100 {
// the if guard mentions a ghost field, so we're now in a ghost context
modify this;
assert x == xx; // fine, since the 'modify' statement only modified ghost fields
assert g == gg; // error: the 'modify' statement can affect the ghost field 'g'
}
}
}
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