Is there HashTable structure in Wolfram Mathematica?

Question

I want to use a Structure like HashTable. Is there similar structure in Wolfram Mathematica?

Answer 1

Mathematica 10 introduces Association, <| k -> v |>,

<|a -> x, b -> y, c -> z|>
%[b]
y

Which is basically a wrapper for a list of rules: Convert a list of rules to an association:

Association[{a -> x, b -> y, c -> z}]
<|a -> x, b -> y, c -> z|>

Convert an association to a list of rules:

Normal[<|a -> x, b -> y, c -> z|>]
{a -> x, b -> y, c -> z}