complement to $

[Steven Schveighoffer]

Currently, D supports the special symbol $ to mean the end of a  
container/range.

However, there is no analogous symbol to mean "beginning of a  
container/range".  For arrays, there is none necessary, 0 is always the  
first element.  But not all containers are arrays.

I'm running into a dilemma for dcollections, I have found a way to make  
all containers support fast slicing (basically by imposing some  
limitations), and I would like to support *both* beginning and end symbols.

Currently, you can slice something in dcollections via:

coll[coll.begin..coll.end];

I could replace that end with $, but what can I replace coll.begin with?   
0 doesn't make sense for things like linked lists, maps, sets, basically  
anything that's not an array.

One thing that's nice about opDollar is I can make it return coll.end, so  
I control the type.  With 0, I have no choice, I must take a uint, which  
means I have to check to make sure it's always zero, and throw an  
exception otherwise.

Would it make sense to have an equivalent symbol for the beginning of a  
container/range?

In regex, ^ matches beginning of the line, $ matches end of the line --  
would there be any parsing ambiguity there?  I know ^ is a binary op, and  
$ means nothing anywhere else, so the two are not exactly equivalent.  I'm  
not very experienced on parsing ambiguities, but things like ~ can be  
unambiguous as binary and unary ops, so maybe it is possible.

So how does this look:  coll[^..$];

Thoughts? other ideas?

-Steve