Best practices for logical const

[Meta]

On Saturday, 15 February 2014 at 12:23:54 UTC, Peter Alexander 
wrote:
> If you want logical const in D, you just don't use const. If 
> you try to hack around it, it will just come back and bite you.
>
> As a result, when writing APIs, don't enforce constness of your 
> parameters if you require logical const. e.g. a range will not 
> necessarily have const front and empty. Trying to enforce that 
> will lead to trouble.

inout is *sort of* logical const, if the underlying type is 
immutable.

T logicalConst(T)(inout(T) t)
{
     //Error: cannot modify inout expression t
     t += 1;
     return t;
}

void main()
{
     auto n = 0;
     auto m = logicalConst(m);
}

The only problem is figuring out if T itself is actually mutable 
and not immutable or const. If you can do that, then it's fine to 
cast inout away and mutate the value.