Add sadd_returns_boolean + sadd? method (#217)

* Add sadd_returns_boolean + sadd? method

* adding comment about said var

Co-authored-by: Michael Bianco <iloveitaly@gmail.com>

lib/redis/namespace.rb

@@ -138,6 +138,7 @@ class Namespace
       "rpush"            => [ :first ],
       "rpushx"           => [ :first ],
       "sadd"             => [ :first ],
+      "sadd?"             => [ :first ],
       "scard"            => [ :first ],
       "scan"             => [ :scan_style, :second ],
       "scan_each"        => [ :scan_style, :all ],
@@ -239,6 +240,13 @@ class Namespace
     # Support 1.8.7 by providing a namespaced reference to Enumerable::Enumerator
     Enumerator = Enumerable::Enumerator unless defined?(::Enumerator)
 
+    # This is used by the Redis gem to determine whether or not to display that deprecation message.
+    @sadd_returns_boolean = true
+
+    class << self
+      attr_accessor :sadd_returns_boolean
+    end
+
     attr_writer :namespace
     attr_reader :redis
     attr_accessor :warning

spec/redis_spec.rb

@@ -358,6 +358,11 @@
     expect(values).to match_array(['banana', 'eggplant'])
   end
 
+  it "should add a new member" do
+    expect(@namespaced.sadd?('foo', 1)).to eq(true)
+    expect(@namespaced.sadd?('foo', 1)).to eq(false)
+  end
+
   it "should add namespace to sort" do
     @namespaced.sadd('foo', 1)
     @namespaced.sadd('foo', 2)