Writing const-correct code in D

[Brad Roberts]

On Thu, 9 Mar 2006, Kevin Bealer wrote:

> The same is true for struct, it gets copied in, which is fine for
> small structs.  For larger structs, you might want to pass by "in *",
> i.e. use "in Foo *".  You can modify this technique to use struct, for
> that see the last item in the numbered list at the end.
> 
> 
> For classes, the issue is that the pointer will not be modified with
> the "in" convention, but the values in the class may be.
> 
> :   this(const_Foo b)
> :   {
> :     x1 = b.x1.dup;
> :   }

I must have missed something somewhere along the way.. when did copying 
imply const?  To me, something that's const can't be modified.  That 
doesn't mean just to the caller, but also to the callee.  It's a mechanism 
for saying "this object shouldn't be changed".  Const by duplication 
doesn't help with the last part and make it entirely probable that code 
will at some point be change to modify parts of the passed in data with 
the expectation that those changes actually occur on up through to the 
caller.

Sorry, const by dup is in some ways even worse than not having const.  I 
see how it solves some usecases though, so it's not totally worse. :)

Later,
Brad