local-variables-hash.rb

def locals(*only, &block)
  raise ArgumentError, "must include a block" unless block_given?
  bndng = block.send(:binding)
  all_locals = eval("local_variables",bndng) - ['_']
  locals_hash = Hash[all_locals.map {|l| [l,eval(l,bndng)]}]
  Hash[locals_hash.select {|k,v| only.include?(v)}]
end

hi = "hello world"
bye = "goodbye world"
locals(hi){} #=> {"hi" => "hello world"}
locals(hi, bye){} #=> {"hi" => "hello world", "bye" => "goodbye world"}

def hash_from_locals(*only, &block)
  raise ArgumentError, "must include a block" unless block_given?
  bndng = block.send(:binding)
  Hash[only.map {|l| [l,eval(l.to_s,bndng)]}]
end
hash_from_locals(:hi, :bye){} #=> {:hi => "hello world", :bye => "goodbye world"}

# Probably the most useful manner... you set some local variables, then you want to build an automatic hash
_first_name = "Daniel"
_last_name = "Parker"

def autohash(&block)
  raise ArgumentError, "must include a block" unless block_given?
  bndng = block.send(:binding)
  all_locals = eval("local_variables",bndng) - ['_']
  locals_hash = Hash[all_locals.map {|l| [l,eval(l,bndng)]}]
  locals_hash.select {|k,v| k.to_s =~ /^_/}.inject({}) {|h,(k,v)| h[k.sub(/^_/,'').to_sym] = v; h}
end

# Generate an automatic hash from all current local_variables that start with '_'
autohash{} #=> {:first_name => "Daniel", :last_name => "Parker"}

# I've thought of renaming this to _hash, so you'd call it as "_hash{}"
# - or, you might like "_locals{}" better...