Ref local variables?

[Simen Kjærås]

On Sun, 08 Jan 2012 18:54:13 +0100, Ben Davis <entheh at cantab.net> 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.id=something;
> 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!
>
> Thanks,
>
> Ben :)

Quick hack:

struct Ref( T ) {
	private:
	T* data;
	public:
	this( ref T value ) {
		data = &value;
	}
	
	ref inout(T) get( ) inout {
		return *data;
	}
	
	alias get this;
}

Ref!T byRef( T )( ref T value ) {
	return Ref!T( value );
}

unittest {
	int a = 3;
	Ref!int b = a;
	b = 4;
	assert( a == 4 );
	
	auto c = byRef( a );
	c = 5;
	assert( a == 5 );
	assert( b == 5 );
}