Custom missing key exception class and full backtrace

.travis.yml

@@ -2,5 +2,6 @@ rvm:
   - 1.8.7
   - 1.9.2
   - 1.9.3
+  - 2.1.2
   # - rbx
   - jruby

README.md

@@ -43,6 +43,14 @@ You can make Hashr raise an `IndexError` though like this:
     config.foo? # => false
     config.foo  # => raises an IndexError "Key :foo is not defined."
 
+Or you can set a custom error class like this:
+    class CustomError < StandardError; ;end
+
+    Hashr.raise_missing_keys = CustomError
+    config = Hashr.new
+    config.foo?  # => false
+    config.foo   # => raises a CustomError "Key :foo is not defined."
+
 You can also anonymously overwrite core Hash methods like this:
 
     config = Hashr.new(:count => 3) do

lib/hashr.rb

@@ -5,6 +5,25 @@ class Hashr < Hash
 
   TEMPLATE = new
 
+  class Keys
+    def initialize(hashr)
+      @hashr, @raise_missing = hashr, hashr.class.raise_missing_keys
+    end
+
+    def fetch!(name)
+      if !@hashr.key?(name) && @raise_missing
+        error_class = @raise_missing.is_a?(Class) ? @raise_missing : IndexError
+        raise(error_class.new("Key #{name.inspect} is not defined.").tap { |e| e.set_backtrace(caller)})
+      else
+        @hashr[name]
+      end
+    end
+
+    def respond_to?(method)
+      @raise_missing ? @hashr.key?(method) : true
+    end
+  end
+
   class << self
     attr_accessor :raise_missing_keys
 
@@ -59,11 +78,7 @@ def set(path, value, stack = [])
   end
 
   def respond_to?(method)
-    if self.class.raise_missing_keys
-      key?(method)
-    else
-      true
-    end
+    Keys.new(self).respond_to?(method)
   end
 
   def method_missing(name, *args, &block)
@@ -73,8 +88,7 @@ def method_missing(name, *args, &block)
     when '='
       self[name.to_s[0..-2].to_sym] = args.first
     else
-      raise(IndexError.new("Key #{name.inspect} is not defined.")) if !key?(name) && self.class.raise_missing_keys
-      self[name]
+      Keys.new(self).fetch!(name)
     end
   end
 

test/hashr_test.rb

@@ -27,6 +27,11 @@ def teardown
     assert_raises(IndexError) { Hashr.new(:foo => 'foo').bar }
   end
 
+  test 'method access on a non-existing key raises a FooError when raise_missing_keys is FooError' do
+    Hashr.raise_missing_keys = FooError
+    assert_raises(FooError) { Hashr.new(:foo => 'foo').bar }
+  end
+
   test 'method access on an existing nested key returns the value' do
     assert_equal 'bar', Hashr.new(:foo => { :bar => 'bar' }).foo.bar
   end

test/test_helper.rb

@@ -2,3 +2,10 @@
 require 'minitest/autorun'
 require 'test_declarative'
 require 'hashr'
+require 'test_support'
+
+module Minitest
+  class Test
+    include TestSupport
+  end
+end

test/test_support.rb

@@ -0,0 +1,4 @@
+module TestSupport
+  class FooError  < StandardError
+  end
+end