From: Gavin Sinclair <gsinclair@...>
Date: 2010-07-17T21:20:04+09:00
Subject: Re: Pstore confusion for a beginner

>
> Questions:
> 1. In this line of code "store[:this] ||= Faunadb.new("")" , what is the
> double pipe equal sign doing? Does it just indicate that the :this
> symbol points to the new Faunadb instance? Why is the double pipe thingy
> not used on the "copy back" code fragment? Would I use the symbol to
> just keep track of what is stored? I know :this is pretty goofy.
>

a ||= b is short for "a = a || b", just like "a += b" is short for "a = a + b".

|| is pronounced "or" (note: Ruby has two similar operators || and
'or' with an important difference -- see any Ruby reference).

a ||= b is equivalent to the following code

if a
  # nothing happens
else
  a = b
end

So store[:this] ||= ...  is saying "if store[:this] doesn't already
exist, set it to...".

>
> 2. In this line of code fdb1=store[:this] from the restore, I noticed
> that it is necessary to have the same symbol :this, in this code
> fragment, as it was in the prior fragment, because I get an error
> otherwise. Is this correct?
>

A PStore object is like a hash.  Imagine you used a hash to store some
name and address details.

hash = {}
hash[:name] = "John Smith"
hash[:address] = "..."

When you wanted to retrieve the name and address, you'd need to use
the same keys :name and :address, wouldn't you?

puts hash[:name]
puts hash[:address]

Hope this helps,
Gavin