Have solution iterators also return enumerators.

Author: gkellogg

lib/rdf/query/solution.rb

@@ -22,6 +22,7 @@ class RDF::Query
   #
   class Solution
     # Undefine all superfluous instance methods:
+    alias_method :__send, :send
     undef_method(*instance_methods.
                   map(&:to_s).
                   select {|m| m.match?(/^\w+$/)}.
@@ -57,29 +58,59 @@ def initialize(bindings = {}, &block)
     # @yieldparam [RDF::Term] value
     # @return [Enumerator]
     def each_binding(&block)
-      @bindings.each(&block)
+      @bindings.each(&block) if block_given?
+      enum_binding
     end
     alias_method :each, :each_binding
 
+    ##
+    # Returns an enumerator for {#each_binding}.
+    #
+    # @return [Enumerator<RDF::Resource>]
+    # @see    #each_subject
+    def enum_binding
+      enum_for(:each_binding)
+    end
+
     ##
     # Enumerates over every variable name in this solution.
     #
     # @yield  [name]
     # @yieldparam [Symbol] name
     # @return [Enumerator]
     def each_name(&block)
-      @bindings.each_key(&block)
+      @bindings.each_key(&block) if block_given?
+      enum_name
     end
     alias_method :each_key, :each_name
 
+    ##
+    # Returns an enumerator for {#each_name}.
+    #
+    # @return [Enumerator<RDF::Resource>]
+    # @see    #each_subject
+    def enum_name
+      enum_for(:each_name)
+    end
+
     ##
     # Enumerates over every variable value in this solution.
     #
     # @yield  [value]
     # @yieldparam [RDF::Term] value
     # @return [Enumerator]
     def each_value(&block)
-      @bindings.each_value(&block)
+      @bindings.each_value(&block) if block_given?
+      enum_value
+    end
+
+    ##
+    # Returns an enumerator for {#each_value}.
+    #
+    # @return [Enumerator<RDF::Resource>]
+    # @see    #each_subject
+    def enum_value
+      enum_for(:each_value)
     end
 
     ##
@@ -101,9 +132,21 @@ def has_variables?(variables)
     # @yieldparam [Variable]
     # @return [Enumerator]
     def each_variable
-      @bindings.each do |name, value|
-        yield Variable.new(name, value)
+      if block_given?
+        @bindings.each do |name, value|
+          yield Variable.new(name, value)
+        end
       end
+      enum_variable
+    end
+
+    ##
+    # Returns an enumerator for {#each_variable}.
+    #
+    # @return [Enumerator<RDF::Resource>]
+    # @see    #each_subject
+    def enum_variable
+      enum_for(:each_variable)
     end
 
     ##
@@ -282,5 +325,19 @@ def method_missing(name, *args, &block)
     def respond_to_missing?(name, include_private = false)
       @bindings.has_key?(name.to_sym) || super
     end
+
+    ##
+    # @private
+    # @param  [Symbol, #to_sym] method
+    # @return [Enumerator]
+    # @see    Object#enum_for
+    def enum_for(method = :each)
+      # Ensure that enumerators are, themselves, queryable
+      this = self
+      Enumerator.new do |yielder|
+        this.__send(method) {|*y| yielder << (y.length > 1 ? y : y.first)}
+      end
+    end
+    alias_method :to_enum, :enum_for
   end # Solution
 end # RDF::Query

lib/rdf/query/variable.rb

@@ -65,13 +65,25 @@ class Variable
     #   the variable name
     # @param  [RDF::Term] value
     #   an optional variable value
-    # @param [Boolean] distinguished (true)
-    #   defaults to false, unless name looks like a bnode
-    def initialize(name = nil, value = nil, distinguished: true, existential: false)
-      @name  = (name || "g#{__id__.to_i.abs}").to_sym
+    # @param [Boolean] distinguished (true) Also interpreted by leading '??' or '$$' in name.
+    # @param [Boolean] existential (true) Also interpreted by leading '$' in name
+    def initialize(name = nil, value = nil, distinguished: nil, existential: nil)
+      name = (name || "g#{__id__.to_i.abs}").to_s
+      if name.start_with?('??')
+        name, dis, ex = name[2..-1], false, false
+      elsif name.start_with?('?')
+        name, dis, ex = name[1..-1], true, false
+      elsif name.start_with?('$$')
+        name, dis, ex = name[2..-1], false, true
+      elsif name.start_with?('$')
+        name, dis, ex = name[1..-1], true, true
+      else
+        dis, ex = true, false
+      end
+      @name = name.to_sym
       @value = value
-      @distinguished = distinguished
-      @existential = existential
+      @distinguished = distinguished.nil? ? dis : distinguished
+      @existential = existential.nil? ? ex : existential
     end
 
     ##