Add spec and doc for class methods

README.md

@@ -61,6 +61,26 @@ a.call { 1 } # => 42
 # Will print because passing a block disables memoization
 ```
 
+For class methods:
+
+```ruby
+class B
+  class << self
+    include Memery
+
+    memoize def call
+      puts "calculating"
+      42
+    end
+  end
+end
+
+B.call # => 42
+B.call # => 42
+B.call # => 42
+# Text will be printed only once.
+```
+
 ## Difference with other gems
 Memery is very similar to [Memoist](https://github.com/matthewrudy/memoist). The difference is that it doesn't override methods, instead it uses Ruby 2 `Module.prepend` feature. This approach is cleaner and it allows subclasses' methods to work properly: if you redefine a memoized method in a subclass, it's not memoized by default, but you can memoize it normally (without using awkward `identifier: ` argument) and it will just work:
 

spec/memery_spec.rb

@@ -57,6 +57,17 @@ class C
   include M
 end
 
+class D
+  class << self
+    include Memery
+
+    memoize def m_args(x, y)
+      CALLS << [x, y]
+      [x, y]
+    end
+  end
+end
+
 RSpec.describe Memery do
   before { CALLS.clear }
   before { B_CALLS.clear }
@@ -132,4 +143,14 @@ class C
       expect(CALLS).to eq([:m])
     end
   end
+
+  context "class method with args" do
+    subject(:d) { D }
+
+    specify do
+      values = [ d.m_args(1, 1), d.m_args(1, 1), d.m_args(1, 2) ]
+      expect(values).to eq([[1, 1], [1, 1], [1, 2]])
+      expect(CALLS).to eq([[1, 1], [1, 2]])
+    end
+  end
 end