• d-bugmail puremagic.com (36/36) Mar 14 2023 https://issues.dlang.org/show_bug.cgi?id=23780

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=23780

          Issue ID: 23780
           Summary: Manual __ctor call can mutate immutable object in
                     safe code
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: snarwin+bugzilla gmail.com

As of DMD 2.102.2, the following program compiles successfully and causes an
assertion failure when run:

---
struct S
{
    int n;
     safe this(int n) immutable { this.n = n; }
}

 safe void main()
{
    immutable S s = 123;
    int before = s.n;
    s.__ctor(456);
    assert(s.n == before); // fails
}
---

The cause of the assertion failure is the mutation of the immutable object `s`
by the call to `S.__ctor`.

Since constructors are allowed to mutate immutable objects for the purpose of
initialization,  safe code must not be allowed to call the constructor of an
existing object, even if that constructor is  safe.

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