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digitalmars.D.bugs - [Issue 11045] New: Pure functions are allowed to read/write global TypeInfo


           Summary: Pure functions are allowed to read/write global
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: maxim maxim-fomin.ru

--- Comment #0 from Maxim Fomin <maxim maxim-fomin.ru> 2013-09-15 13:35:15 PDT
Apparently dmd does not protect TypeInfos from reading/mutating from pure

import core.stdc.string, std.stdio;

pure hijack(T)(T value) if (is(T == class)) 
    byte[] init_mem = new byte[T.classinfo.init.length];
    memcpy(init_mem.ptr, cast(byte*)value, T.classinfo.init.length);
    T.classinfo.init = init_mem;

class A
   int a;

pure foo(int val) 
   A a = new A;
   return a.a + val;

void main()
   writeln(0.foo, 0.foo, 0.foo);

Prints there different results for the same arguments.

However on the other hand, it makes sense to allow reading some read-only
typeinfo values - it can be treated the same as reading module-level immutable

Why TypeInfo should be mutable per se is a good question too.

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Sep 15 2013