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digitalmars.D.bugs - [Issue 21669] New: closure over type with destructor allows


          Issue ID: 21669
           Summary: closure over type with destructor allows accessing
                    destroyed value if used after scope exits
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: schveiguy gmail.com

An example:

import std.stdio;
struct S
   int i;
   ~this() { i = -1;}

void main()
   int delegate() dg;
      S s;
      dg = () { return s.i; };
      writeln(dg()); // 0
   writeln(dg()); // -1

Allowing access to a destroyed variable where a destructor has invalidated the
object should not be allowed. Prior to 2.053, this was an error. According to
Paul Backus, the responsible PR was this:

One who has created a delegate would probably expect that when calling the
delegate at a later time, the state of the object should be preserved, and not
destroyed. For some cases, it might be dangerous safety-wise to use an object
after destruction.

Fixing this issue probably requires a long deprecation period, as no doubt code
that depends on this (or works in spite of the dangers) exists today.

Feb 27 2021