Populate Wildcards

gistfile1.rb

# if you're interested, you can follow the conversation around how to make `populate_wildcards` 
# more idiomatic on /r/ruby:
# https://www.reddit.com/r/ruby/comments/2iyzab/is_there_a_more_idiomatic_andor_functional_way_to/

# my initial approach

def populate_wildcards(a,b)
  a.merge(b) { |key, left, right|
    if left.is_a? Hash
      populate_wildcards(left, right)
    elsif left.is_a? Array
      left.zip(right).map do |_left, _right|
        populate_wildcards _left, _right
      end
    else
      if left == '*'
        right
      else
        left
      end
    end
  }
end

start_hash = {a: '*', c: {d: '*', f: 'g'}}
other_hash = {a: 'b', c: {d: 'e', f: 'g'}}

result = populate_wildcards(start_hash, other_hash)
result == other_hash #=> true

============================

# @joelparkerhenderson's approach 

class Hash
  def merge_using_wildcard(other_hash)
    merge(other_hash){|key, oldval, newval|
      case oldval
      when Hash
        oldval.merge_using_wildcard(newval)
      when '*'
        newval
      else
        oldval
      end
    }
  end
end

start_hash = {a: '*', c: {d: '*', f: 'g'}}
other_hash = {a: 'b', c: {d: 'e', f: 'g'}}

result = start_hash.merge_using_wildcard(other_hash)
result == other_hash #=> true

============================

# @zeringus' approach

def apply_defaults givens, defaults, wildcard = '*'
  givens.merge defaults do |_key, given, default|
    if given.is_a? Hash
      apply_defaults given, default
    else
      given == wildcard ? default : given
    end
  end
end

start_hash = {a: '*', c: {d: '*', f: 'g'}}
other_hash = {a: 'b', c: {d: 'e', f: 'g'}}

result = apply_defaults(other_hash, start_hash)
result == other_hash #=> true

============================

# @revdan's approach

class Wildcard < Struct.new(:hash, :definitions)
  def compare(a = hash, b = definitions)
    a.merge(b) do |_, left, right|
      if left.is_a? Hash
        compare(left, right)
      else
        left == '*' ? right : left
      end
    end
  end
end
 
Wildcard.new(
  {:foo=>"*", :bar=>{:baz=>"*", :buck=>"buck"}},
  {:foo=>"bar", :bar=>{:baz=>"baz", :buck=>"buck"}}
).compare