Reflect write to embeded structs

internal/reflectbuild/reflectbuild.go

@@ -8,6 +8,13 @@ import (
 	"strings"
 )
 
+// fieldGetters are functions that given a struct return a specific field
+// (likely captured in their scope)
+type fieldGetter func(s reflect.Value) reflect.Value
+
+// collection of fieldGetters for a given struct type
+type structFieldGetters map[string]fieldGetter
+
 // Builder wraps a value and provides method to modify its structure.
 // It is a stateful object that keeps a cursor of what part of the object is
 // being modified.
@@ -17,11 +24,89 @@ type Builder struct {
 	// Root is always a pointer to a non-nil value.
 	// Cursor is the top of the stack.
 	stack []reflect.Value
+	// Struct field tag to use to retrieve name.
+	nameTag string
+	// Cache of functions to access specific fields.
+	fieldGettersCache map[reflect.Type]structFieldGetters
+}
+
+func copyAndAppend(s []int, i int) []int {
+	ns := make([]int, len(s)+1)
+	copy(ns, s)
+	ns[len(ns)-1] = i
+	return ns
+}
+
+func (b *Builder) getOrGenerateFieldGettersRecursive(m structFieldGetters, idx []int, s reflect.Type) {
+	for i := 0; i < s.NumField(); i++ {
+		f := s.Field(i)
+		if f.PkgPath != "" {
+			// only consider exported fields
+			continue
+		}
+		// TODO: handle embedded structs
+		if f.Anonymous {
+			b.getOrGenerateFieldGettersRecursive(m, copyAndAppend(idx, i), f.Type)
+		} else {
+			fieldName, ok := f.Tag.Lookup(b.nameTag)
+			if !ok {
+				fieldName = f.Name
+			}
+
+			if len(idx) == 0 {
+				m[fieldName] = makeFieldGetterByIndex(i)
+			} else {
+				m[fieldName] = makeFieldGetterByIndexes(copyAndAppend(idx, i))
+			}
+		}
+	}
+
+	if b.fieldGettersCache == nil {
+		b.fieldGettersCache = make(map[reflect.Type]structFieldGetters, 1)
+	}
+
+	b.fieldGettersCache[s] = m
+}
+
+func (b *Builder) getOrGenerateFieldGetters(s reflect.Type) structFieldGetters {
+	if s.Kind() != reflect.Struct {
+		panic("generateFieldGetters can only be called on a struct")
+	}
+	m, ok := b.fieldGettersCache[s]
+	if ok {
+		return m
+	}
+
+	m = make(structFieldGetters, s.NumField())
+	b.getOrGenerateFieldGettersRecursive(m, nil, s)
+	b.fieldGettersCache[s] = m
+	return m
+}
+
+func makeFieldGetterByIndex(idx int) fieldGetter {
+	return func(s reflect.Value) reflect.Value {
+		return s.Field(idx)
+	}
+}
+
+func makeFieldGetterByIndexes(idx []int) fieldGetter {
+	return func(s reflect.Value) reflect.Value {
+		return s.FieldByIndex(idx)
+	}
+}
+
+func (b *Builder) fieldGetter(t reflect.Type, s string) (fieldGetter, error) {
+	m := b.getOrGenerateFieldGetters(t)
+	g, ok := m[s]
+	if !ok {
+		return nil, fmt.Errorf("field '%s' not accessible on '%s'", s, t)
+	}
+	return g, nil
 }
 
 // NewBuilder creates a Builder to construct v.
 // If v is nil or not a pointer, an error will be returned.
-func NewBuilder(v interface{}) (Builder, error) {
+func NewBuilder(tag string, v interface{}) (Builder, error) {
 	if v == nil {
 		return Builder{}, fmt.Errorf("cannot build a nil value")
 	}
@@ -32,8 +117,9 @@ func NewBuilder(v interface{}) (Builder, error) {
 	}
 
 	return Builder{
-		root:  rv.Elem(),
+		root:    rv.Elem(),
-		stack: []reflect.Value{rv.Elem()},
+		stack:   []reflect.Value{rv.Elem()},
+		nameTag: tag,
 	}, nil
 }
 
@@ -90,7 +176,12 @@ func (b *Builder) DigField(s string) error {
 		return err
 	}
 
-	f := t.FieldByName(s)
+	g, err := b.fieldGetter(t.Type(), s)
+	if err != nil {
+		return err
+	}
+
+	f := g(t)
 	if !f.IsValid() {
 		return FieldNotFoundError{FieldName: s, Struct: t}
 	}

internal/reflectbuild/reflectbuild_test.go

@@ -11,17 +11,17 @@ import (
 
 func TestNewBuilderSuccess(t *testing.T) {
 	x := struct{}{}
-	_, err := reflectbuild.NewBuilder(&x)
+	_, err := reflectbuild.NewBuilder("", &x)
 	assert.NoError(t, err)
 }
 
 func TestNewBuilderNil(t *testing.T) {
-	_, err := reflectbuild.NewBuilder(nil)
+	_, err := reflectbuild.NewBuilder("", nil)
 	assert.Error(t, err)
 }
 
 func TestNewBuilderNonPtr(t *testing.T) {
-	_, err := reflectbuild.NewBuilder(struct{}{})
+	_, err := reflectbuild.NewBuilder("", struct{}{})
 	assert.Error(t, err)
 }
 
@@ -29,7 +29,7 @@ func TestDigField(t *testing.T) {
 	x := struct {
 		Field string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	assert.Error(t, b.DigField("oops"))
 	assert.NoError(t, b.DigField("Field"))
@@ -41,7 +41,7 @@ func TestBack(t *testing.T) {
 		A string
 		B string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	b.Save()
 	assert.NoError(t, b.DigField("A"))
@@ -63,7 +63,7 @@ func TestReset(t *testing.T) {
 		A []string
 		B string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	require.NoError(t, b.DigField("A"))
 	require.NoError(t, b.SliceNewElem())
@@ -80,7 +80,7 @@ func TestSetString(t *testing.T) {
 	x := struct {
 		Field string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	assert.Error(t, b.SetString("oops"))
 	require.NoError(t, b.DigField("Field"))
@@ -92,7 +92,7 @@ func TestSliceNewElem(t *testing.T) {
 	x := struct {
 		Field []string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	require.NoError(t, b.DigField("Field"))
 	b.Save()
@@ -112,7 +112,7 @@ func TestSliceNewElemNested(t *testing.T) {
 	x := struct {
 		Field [][]string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	require.NoError(t, b.DigField("Field"))
 
@@ -159,7 +159,7 @@ func TestCursor(t *testing.T) {
 	x := struct {
 		Field string
 	}{}
-	b, err := reflectbuild.NewBuilder(&x)
+	b, err := reflectbuild.NewBuilder("", &x)
 	require.NoError(t, err)
 	assert.Equal(t, b.Cursor().Kind(), reflect.Struct)
 	require.NoError(t, b.DigField("Field"))

unmarshal.go

@@ -8,7 +8,7 @@ import (
 
 func Unmarshal(data []byte, v interface{}) error {
 	u := &unmarshaler{}
-	u.builder, u.err = reflectbuild.NewBuilder(v)
+	u.builder, u.err = reflectbuild.NewBuilder("toml", v)
 	if u.err == nil {
 		parseErr := parser{builder: u}.parse(data)
 		if parseErr != nil {