Bug 11045 – Pure functions are allowed to read/write global TypeInfo

Apparently dmd does not protect TypeInfos from reading/mutating from pure functions. 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; a.a++; hijack(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 variable. Why TypeInfo should be mutable per se is a good question too.

I cannot reproduce this because the examples has some errors in it. If you can provide a compilable updated example, then please reopen this.