Ref local variables?

Steven Schveighoffer schveiguy at
Mon Jan 9 06:13:07 PST 2012

On Sun, 08 Jan 2012 12:54:13 -0500, Ben Davis <entheh at> wrote:

> Hi,
> Is there a reason 'ref' is disallowed for local variables? I want to  
> write something like:
> MapTile[] map;	// It's a struct
> ref MapTile tile=map[y*w+x];
> tile.isWall=true;
> My actual case is more complicated, so inlining the expression  
> everywhere would be messy. I can't use 'with' because I sometimes pass  
> 'tile' to a function (which also takes it as a ref). I don't want to  
> make it a class since the array is quite big and that would be a lot of  
> extra overhead. For now I'm using pointers, but this is forcing me to  
> insert & or * operators sometimes, and it also reduces the temptation to  
> use 'ref' in the places where it IS allowed, since it's inconsistent.
> I hope it's not a stupid question - it's my first one - but I couldn't  
> find an answer anywhere. I like most of what I've seen of D so far, and  
> I'm very glad to be able to leave C and C++ (mostly) behind!

My first inclination is to use pointers.  D doesn't have -> operator, so  
pointers are seamless for your small example:

auto tile = &map[y*w+x]; = something;
tile.isWall = true;

When you need to pass it to a ref function, or if you do any operators on  
it, you would need to use *.

Another horribly inefficient option (if you don't use -inline) is this:

@property ref tile() { return map[y*w+x]; }

With new => syntax (in git head), this would probably be:

@property ref tile => map[y*w+x];


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