Implement non-destructive hash methods

When calling the following non-destructive hash methods:
:compact
:invert
:reject
:select
:slice
:transform_keys
:transform_values
we would be returned an instance of a standard Hash rather
than a Mash (or subclass). This changes that behavior to
instead return an instance of the class the method was
called on.

1 files changed, 42 insertions, 0 deletions

diff --git a/lib/hashie/mash.rb b/lib/hashie/mash.rb
index 06cef59..bac93a4 100644
--- a/lib/hashie/mash.rb
+++ b/lib/hashie/mash.rb
@@ -207,6 +207,31 @@ module Hashie
       super(*keys.map { |key| convert_key(key) })
     end
 
+    # Returns a new instance of the class it was called on, with nil values
+    # removed.
+    def compact
+      self.class.new(super)
+    end
+
+    # Returns a new instance of the class it was called on, using its keys as
+    # values, and its values as keys. The new values and keys will always be
+    # strings.
+    def invert
+      self.class.new(super)
+    end
+
+    # Returns a new instance of the class it was called on, containing elements
+    # for which the given block returns false.
+    def reject(&blk)
+      self.class.new(super(&blk))
+    end
+
+    # Returns a new instance of the class it was called on, containing elements
+    # for which the given block returns true.
+    def select(&blk)
+      self.class.new(super(&blk))
+    end
+
     alias regular_dup dup
     # Duplicates the current mash as a new mash.
     def dup
@@ -320,6 +345,23 @@ module Hashie
       end
     end
 
+    with_minimum_ruby('2.4.0') do
+      def transform_values(&blk)
+        self.class.new(super(&blk))
+      end
+    end
+
+    with_minimum_ruby('2.5.0') do
+      def slice(*keys)
+        string_keys = keys.map { |key| convert_key(key) }
+        self.class.new(super(*string_keys))
+      end
+
+      def transform_keys(&blk)
+        self.class.new(super(&blk))
+      end
+    end
+
     protected
 
     def method_name_and_suffix(method_name)