Implicit conversion of struct with methods to immutable in pure function fails

[Simen Kjærås]

On Wednesday, 18 July 2018 at 11:28:54 UTC, Timoses wrote:
> But why is a context pointer a problem? Is it problematic 
> because the context pointer to the main scope can not guarantee 
> `immutable`? E.g. if I happened to use data from main in a 
> function of the immutable struct then... well then what?
> The struct would still be immutable, but what would prevent a 
> function from using non-immutable data?

It's a known bug: https://issues.dlang.org/show_bug.cgi?id=18563
In the associated discussion 
(https://forum.dlang.org/thread/p7lp2b$1jod$1@digitalmars.com), 
Steven Schveighoffer points out that an immutable struct may be 
passed to other threads, which would give one thread access to 
another thread's stack. This could be a good enough reason to 
prevent this kind of conversion, but a better error message would 
still make sense.

--
   Simen