[D2] const vs structs

[Steven Schveighoffer]

On Thu, 10 Dec 2009 19:23:43 -0500, Richard Webb <webby at beardmouse.org.uk>  
wrote:

> I just tried to build the Juno library with DMD 2.037, and got a bunch  
> or errors like:
>
> juno\com\core.d(295): Error: function juno.com.core.GUID.opEquals type  
> signature should be const bool(ref const(GUID)) not bool(GUID other)
>
> Which can be replicated with:
> ////////////////////////////////
> struct Foo
> {
> 	bool opEquals(Foo f) const
> 	{
> 		return true;
> 	}
> }
>
> void Bar()
> {
> 	Foo f;
> }
> ////////////////////////////////
>
> It built ok with DMD2 a few months ago. Is this an intentional change?

It's due to this change: http://www.dsource.org/projects/dmd/changeset/260

The issue being fixed was this:

http://d.puremagic.com/issues/show_bug.cgi?id=3433

I think it should be a bug, because your opEquals does not violate const,  
since you are making a copy of a Foo, and Foo contains no references.   
Please file a bug and reference 3433 and changeset 260.  I think it should  
be allowed to have a signature like this:

bool opEquals(T other) const

inside T as long as T can be implicitly cast from const to mutable.

>
> Also, while looking at the problem i noticed that code like:
>
> ////////////////////////////////
> struct Foo
> {
> 	~this()
> 	{
> 		
> 	}
> }
>
> void Bar()
> {
> 	const Foo f;
> }
> ////////////////////////////////
>
> Produces the error:
>
> Error: destructor Foo.~this () is not callable using argument types ()
>
> which seems a bit wrong?
>

Yeah, that's weird.  Probably something to do with const.  Probably should  
file another bug :)

-Steve