Better handling of casting with covariance and contravariance

src/spectator/mocks/double.cr

@@ -41,11 +41,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         @spectator_stub_calls << %call
         if (%stub = @spectator_stubs.find(&.callable?(%call)))
-          if (%cast = %stub.as?(::Spectator::Mocks::GenericMethodStub(typeof(%method({{args.splat}})))))
+          %stub.call(%args, typeof(%method({{args.splat}})))
-            %cast.call(%args)
-          else
-            raise "The return type of stub #{%stub} doesn't match the expected type #{typeof(%method({{args.splat}}))}"
-          end
         else
           %method({{args.splat}})
         end
@@ -56,11 +52,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         @spectator_stub_calls << %call
         if (%stub = @spectator_stubs.find(&.callable?(%call)))
-          if (%cast = %stub.as?(::Spectator::Mocks::GenericMethodStub(typeof(%method({{args.splat}}) { |*%yield_args| yield *%yield_args }))))
+          %stub.call(%args, typeof(%method({{args.splat}}) { |*%ya| yield *%ya }))
-            %cast.call(%args)
-          else
-            raise "The return type of stub #{%stub} doesn't match the expected type #{typeof(%method({{args.splat}}) { |*%ya| yield *%ya })}"
-          end
         else
           %method({{args.splat}}) do |*%yield_args|
             yield *%yield_args

src/spectator/mocks/generic_method_stub.cr

@@ -13,8 +13,6 @@ module Spectator::Mocks
       super && (!@args || @args === call.args)
     end
 
-    abstract def call(args : GenericArguments(T, NT)) : ReturnType forall T, NT
-
     def to_s(io)
       super(io)
       if @args

src/spectator/mocks/method_stub.cr

@@ -10,6 +10,8 @@ module Spectator::Mocks
       @name == call.name
     end
 
+    abstract def call(args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
+
     def to_s(io)
       io << '#'
       io << @name

src/spectator/mocks/nil_method_stub.cr

@@ -4,8 +4,12 @@ require "./value_method_stub"
 
 module Spectator::Mocks
   class NilMethodStub < GenericMethodStub(Nil)
-    def call(_args : GenericArguments(T, NT)) : Nil forall T, NT
+    def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
-      nil
+      if (cast = nil.as?(RT))
+        cast
+      else
+        raise "The return type of stub #{to_s} : Nil doesn't match the expected type #{RT}"
+      end
     end
 
     def and_return(value : T) forall T

src/spectator/mocks/proc_method_stub.cr

@@ -7,8 +7,13 @@ module Spectator::Mocks
       super(name, source, args)
     end
 
-    def call(_args : GenericArguments(T, NT)) : ReturnType forall T, NT
+    def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
-      @proc.call
+      result = @proc.call
+      if (cast = result.as?(RT))
+        cast
+      else
+        raise "The return type of stub #{to_s} : #{ReturnType} doesn't match the expected type #{RT}"
+      end
     end
   end
 end

src/spectator/mocks/value_method_stub.cr

@@ -7,8 +7,13 @@ module Spectator::Mocks
       super(name, source, args)
     end
 
-    def call(_args : GenericArguments(T, NT)) : ReturnType forall T, NT
+    def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
-      @value
+      result = @value
+      if (cast = result.as?(RT))
+        cast
+      else
+        raise "The return type of stub #{to_s} : #{ReturnType} doesn't match the expected type #{RT}"
+      end
     end
   end
 end