is my code to get CTFE instantiated object valid D ?

[chmike via Digitalmars-d-learn]

On Friday, 27 May 2016 at 21:41:02 UTC, Kagamin wrote:
> On Friday, 27 May 2016 at 20:20:36 UTC, chmike wrote:
>> Is this code valid D or is the behavior undefined due to the 
>> cast ?
>
> A mutable object can be synchronized on:
> synchronized(Category.instance){}
> This will create and store a mutex in the object (sad but true, 
> design taken from java). If the immutable object is in readonly 
> memory, it will crash on write.

That is a good argument. Thanks. It would indeed be a good idea 
to put immutable objects in a read only portion of the code.

Would it be different if the object was declared const instead of 
immutable ?

I want compile time instantiation and mutable references to the 
object. Apparently only immutable and const objects can be 
instantiated at compile time. I also want an app wide singleton 
(not stored in TLS). If I use _gshared I apparently wouldn't get 
a compile time instantitation.

It's to implement the flyweight pattern. I don't want to use 
Rebindable because the assembly code generated by dmd is 
currently inefficient. Rebindable cast away the const but the non 
constant reference is not exposed.

What is the difference between a const and immutable object ? 
would a const object be allowed to modify itself by using a hash 
table or caching results inside ? Is a static const Category c 
variable a TLS variable ?

This is a bit frustrating because it is trivial to implement in C 
and C++.