Why can't a Regex object be immutable?

[cym13 via Digitalmars-d-learn]

On Saturday, 2 January 2016 at 02:03:13 UTC, Shriramana Sharma 
wrote:
> Shriramana Sharma wrote:
>
>> Why is it impossible for a Regex object to be
>> `immutable`?
>
> I find that I can't declare it as `const` either... This is 
> most curious!

I think it's because regex() only compiles the regex at runtime 
so it needs to be modified later ; you'll find that using 
ctRegex() instead will allow you to declare it immutable for 
example. I didn't look at the implementation to identify a 
precise cause though.