add InvokeOption for Names

addesses uber-go#181

dig.go

@@ -65,6 +65,7 @@ type provideOptions struct {
 	Info     *ProvideInfo
 	As       []interface{}
 	Location *digreflect.Func
+	Names    []string
 }
 
 func (o *provideOptions) Validate() error {
@@ -282,10 +283,40 @@ func LocationForPC(pc uintptr) ProvideOption {
 	})
 }
 
+type invokeOptions struct {
+	Names []string
+}
+
+func (*invokeOptions) Validate() error {
+	return nil
+}
+
 // An InvokeOption modifies the default behavior of Invoke. It's included for
 // future functionality; currently, there are no concrete implementations.
 type InvokeOption interface {
-	unimplemented()
+	applyInvokeOption(*invokeOptions)
+}
+
+type invokeOptionFunc func(*invokeOptions)
+
+func (f invokeOptionFunc) applyInvokeOption(opts *invokeOptions) { f(opts) }
+
+type InvokeAndProvideOption interface {
+	InvokeOption
+	ProvideOption
+}
+
+type namesOption []string
+
+func (n namesOption) applyInvokeOption(opts *invokeOptions) {
+	opts.Names = n
+}
+func (n namesOption) applyProvideOption(opts *provideOptions) {
+	opts.Names = n
+}
+
+func Names(names ...string) InvokeAndProvideOption {
+	return namesOption(names)
 }
 
 // Container is a directed acyclic graph of types and their dependencies.
@@ -566,7 +597,15 @@ func (c *Container) Invoke(function interface{}, opts ...InvokeOption) error {
 		return errf("can't invoke non-function %v (type %v)", function, ftype)
 	}
 
-	pl, err := newParamList(ftype)
+	var options invokeOptions
+	for _, o := range opts {
+		o.applyInvokeOption(&options)
+	}
+	if err := options.Validate(); err != nil {
+		return err
+	}
+
+	pl, err := newParamList(ftype, options.Names)
 	if err != nil {
 		return err
 	}
@@ -624,6 +663,7 @@ func (c *Container) provide(ctor interface{}, opts provideOptions) error {
 			ResultGroup: opts.Group,
 			ResultAs:    opts.As,
 			Location:    opts.Location,
+			ParamNames:  opts.Names,
 		},
 	)
 	if err != nil {
@@ -842,14 +882,15 @@ type nodeOptions struct {
 	ResultGroup string
 	ResultAs    []interface{}
 	Location    *digreflect.Func
+	ParamNames  []string
 }
 
 func newNode(ctor interface{}, opts nodeOptions) (*node, error) {
 	cval := reflect.ValueOf(ctor)
 	ctype := cval.Type()
 	cptr := cval.Pointer()
 
-	params, err := newParamList(ctype)
+	params, err := newParamList(ctype, opts.ParamNames)
 	if err != nil {
 		return nil, err
 	}

dig_test.go

@@ -536,6 +536,45 @@ func TestEndToEndSuccess(t *testing.T) {
 		}), "invoke should succeed, pulling out two named instances")
 	})
 
+	t.Run("named instances can be used to Provide another instance", func(t *testing.T) {
+		c := New()
+
+		type A struct{ idx int }
+
+		buildConstructor := func(idx int) func() A {
+			return func() A { return A{idx: idx} }
+		}
+
+		require.NoError(t, c.Provide(buildConstructor(1), Name("first")))
+		require.NoError(t, c.Provide(buildConstructor(2), Name("second")))
+		require.NoError(t, c.Provide(func(a A) int {
+			return a.idx + 5
+		}, Names("first")))
+
+		require.NoError(t, c.Invoke(func(i int) {
+			assert.Equal(t, 6, i)
+		}), "invoke should succeed, pulling out one named instances")
+	})
+
+	t.Run("named instances can be invoked Name option", func(t *testing.T) {
+		c := New()
+
+		type A struct{ idx int }
+
+		buildConstructor := func(idx int) func() A {
+			return func() A { return A{idx: idx} }
+		}
+
+		require.NoError(t, c.Provide(buildConstructor(1), Name("first")))
+		require.NoError(t, c.Provide(buildConstructor(2), Name("second")))
+		require.NoError(t, c.Provide(buildConstructor(3), Name("third")))
+
+		require.NoError(t, c.Invoke(func(a1 A, a3 A) {
+			assert.Equal(t, 1, a1.idx)
+			assert.Equal(t, 3, a3.idx)
+		}, Names("first", "third")), "invoke should succeed, using two named instances")
+	})
+
 	t.Run("named and unnamed instances coexist", func(t *testing.T) {
 		c := New()
 		type A struct{ idx int }
@@ -561,6 +600,25 @@ func TestEndToEndSuccess(t *testing.T) {
 		}))
 	})
 
+	t.Run("named and unnamed instances can be invoked with Names option", func(t *testing.T) {
+		c := New()
+
+		type A struct{ idx int }
+
+		buildConstructor := func(idx int) func() A {
+			return func() A { return A{idx: idx} }
+		}
+
+		require.NoError(t, c.Provide(buildConstructor(1), Name("first")))
+		require.NoError(t, c.Provide(buildConstructor(2), Name("second")))
+		require.NoError(t, c.Provide(buildConstructor(3)))
+
+		require.NoError(t, c.Invoke(func(a1 A, a3 A) {
+			assert.Equal(t, 1, a1.idx)
+			assert.Equal(t, 3, a3.idx)
+		}, Names("first")), "invoke should succeed, using two named instances")
+	})
+
 	t.Run("named instances recurse", func(t *testing.T) {
 		c := New()
 		type A struct{ idx int }

param.go

@@ -62,11 +62,14 @@ var (
 
 // newParam builds a param from the given type. If the provided type is a
 // dig.In struct, an paramObject will be returned.
-func newParam(t reflect.Type) (param, error) {
+func newParam(t reflect.Type, paramName string) (param, error) {
 	switch {
 	case IsOut(t) || (t.Kind() == reflect.Ptr && IsOut(t.Elem())) || embedsType(t, _outPtrType):
 		return nil, errf("cannot depend on result objects", "%v embeds a dig.Out", t)
 	case IsIn(t):
+		if paramName != "" {
+			return nil, errf("cannot have a paramName (%s) with a struct that has dig.In", paramName)
+		}
 		return newParamObject(t)
 	case embedsType(t, _inPtrType):
 		return nil, errf(
@@ -77,7 +80,7 @@ func newParam(t reflect.Type) (param, error) {
 			"cannot depend on a pointer to a parameter object, use a value instead",
 			"%v is a pointer to a struct that embeds dig.In", t)
 	default:
-		return paramSingle{Type: t}, nil
+		return paramSingle{Type: t, Name: paramName}, nil
 	}
 }
 
@@ -158,7 +161,7 @@ func (pl paramList) DotParam() []*dot.Param {
 //
 // Variadic arguments of a constructor are ignored and not included as
 // dependencies.
-func newParamList(ctype reflect.Type) (paramList, error) {
+func newParamList(ctype reflect.Type, names []string) (paramList, error) {
 	numArgs := ctype.NumIn()
 	if ctype.IsVariadic() {
 		// NOTE: If the function is variadic, we skip the last argument
@@ -171,8 +174,16 @@ func newParamList(ctype reflect.Type) (paramList, error) {
 		Params: make([]param, 0, numArgs),
 	}
 
+	if numArgs < len(names) {
+		return pl, errf("can't create a constructor with more names=%s than args=%s", names, ctype)
+	}
+
 	for i := 0; i < numArgs; i++ {
-		p, err := newParam(ctype.In(i))
+		name := ""
+		if i < len(names) {
+			name = names[i]
+		}
+		p, err := newParam(ctype.In(i), name)
 		if err != nil {
 			return pl, errf("bad argument %d", i+1, err)
 		}
@@ -370,7 +381,7 @@ func newParamObjectField(idx int, f reflect.StructField) (paramObjectField, erro
 
 	default:
 		var err error
-		p, err = newParam(f.Type)
+		p, err = newParam(f.Type, "")
 		if err != nil {
 			return pof, err
 		}

param_test.go

@@ -30,7 +30,7 @@ import (
 )
 
 func TestParamListBuild(t *testing.T) {
-	p, err := newParamList(reflect.TypeOf(func() io.Writer { return nil }))
+	p, err := newParamList(reflect.TypeOf(func() io.Writer { return nil }), []string{})
 	require.NoError(t, err)
 	assert.Panics(t, func() {
 		p.Build(New())
@@ -238,7 +238,7 @@ func TestParamVisitorChecksEverything(t *testing.T) {
 
 	pl, err := newParamList(reflect.TypeOf(func(io.Reader, params, io.Writer) {
 		t.Fatalf("this function should not be called")
-	}))
+	}), []string{})
 	require.NoError(t, err)
 
 	idx := 0