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class A {
method M() {
var y := new A[100];
y[5] := null;
}
method N0() {
var a: array<int>;
if (a != null && 5 < a.Length) {
a[5] := 12; // error: violates modifies clause
}
}
method N1(a: array<int>)
modifies a;
{
var b := a.Length; // error: a may be null
}
method N2(a: array<int>)
requires a != null;
modifies a;
{
a[5] := 12; // error: index may be outside bounds
}
method N3(a: array<int>)
requires a != null && 5 < a.Length;
modifies a;
ensures (forall i :: 0 <= i && i < a.Length ==> a[i] == old(a[i]) || (i == 5 && a[i] == 12));
{
a[5] := 12; // all is good
}
var zz0: array<A>;
var zz1: array<B>;
method O() {
var zz2 := new A[25];
assert zz2 != zz0; // holds because zz2 is newly allocated
var o: object := zz0;
assert this != o; // holds because zz0 has a different type
/****** This would be a good thing to be able to verify, but the current encoding is not up to the task
if (zz0 != null && zz1 != null && 2 <= zz0.Length && zz0.Length == zz1.Length) {
o := zz1[1];
assert zz0[1] == o ==> o == null; // holds because zz0 and zz1 have different element types
}
******/
assert zz2[20] == null; // error: no reason that this must hold
}
var x: array<int>;
method P0()
modifies this;
{
if (x != null && 100 <= x.Length) {
x[5] := 12; // error: violates modifies clause
}
}
method P1()
modifies this`x;
{
if (x != null && 100 <= x.Length) {
x[5] := 12; // error: violates modifies clause
}
}
method P2()
modifies x;
{
if (x != null && 100 <= x.Length) {
x[5] := 12; // fine
}
}
method Q() {
var a := new int[5];
a[0],a[1],a[2],a[3],a[4] := 0,1,2,3,4;
assert [1,2,3,4] == a[1..];
assert [1,2,3,4] == a[1.. a.Length];
assert [1] == a[1..2];
assert [0,1] == a[..2];
assert [0,1] == a[0..2];
assert forall i :: 0 <= i <= a.Length ==> [] == a[i..i];
assert [0,1,2,3,4] == a[..];
assert forall i :: 0 <= i < a.Length ==> a[i] == i;
}
}
class B { }
// -------------------------------
class ArrayTests {
function F0(a: array<int>): bool
{
a != null && 10 <= a.Length &&
a[7] == 13 // error: reads on something outside reads clause
}
var b: array<int>;
function F1(): bool
reads this;
{
b != null && 10 <= b.Length &&
b[7] == 13 // error: reads on something outside reads clause
}
function F2(a: array<int>): bool
reads this, b, a;
{
a != null && 10 <= a.Length &&
a[7] == 13 // good
&&
b != null && 10 <= b.Length &&
b[7] == 13 // good
}
method M0(a: array<int>)
requires a != null && 10 <= a.Length;
{
a[7] := 13; // error: updates location not in modifies clause
}
method M1()
requires b != null && 10 <= b.Length;
modifies this;
{
b[7] := 13; // error: updates location not in modifies clause
}
method M2()
modifies this;
{
var bb := new int[75];
b := bb; // fine
}
method M3(a: array<int>)
requires a != null && 10 <= a.Length;
requires b != null && 10 <= b.Length;
modifies this, b, a;
{
a[7] := 13; // good
b[7] := 13; // good
}
}
// -------------------- induction attribute --------------------------------
ghost method Fill_I(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j {:induction i} :: 0 <= i < j < |s| ==> s[i] <= s[j];
{ // error: cannot prove postcondition
}
ghost method Fill_J(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j {:induction j} :: 0 <= i < j < |s| ==> s[i] <= s[j];
{
}
ghost method Fill_All(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j {:induction i,j} :: 0 <= i < j < |s| ==> s[i] <= s[j];
{
}
ghost method Fill_True(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j {:induction} :: 0 <= i < j < |s| ==> s[i] <= s[j];
{
}
ghost method Fill_False(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j {:induction false} :: 0 <= i < j < |s| ==> s[i] <= s[j];
{ // error: cannot prove postcondition
}
ghost method Fill_None(s: seq<int>)
requires forall i :: 1 <= i < |s| ==> s[i-1] <= s[i];
ensures forall i,j :: 0 <= i < j < |s| ==> s[i] <= s[j];
{ // error: cannot prove postcondition
}
// -------------- some regression tests; there was a time when array-element LHSs of calls were not translated correctly
method Test_ArrayElementLhsOfCall(a: array<int>, i: int, c: Cdefg<int>) returns (x: int)
requires a != null && c != null;
modifies a, c;
{
if (0 <= i < a.Length) {
a[i] := x;
a[i] := Test_ArrayElementLhsOfCall(a, i-1, c); // this line used to crash Dafny
c.t := x;
c.t := Test_ArrayElementLhsOfCall(a, i-1, c); // this line used to crash Dafny
var n: nat;
n := x; // error: subrange check is applied and it cannot be verified
n := Test_ArrayElementLhsOfCall(a, i-1, c); // error: subrange check is applied and it cannot be verified
}
}
class Cdefg<T> {
var t: T;
}
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