Introduce fluent.Reflect convenience method.

fluent/reflect.go

+package fluent
+
+import (
+	"fmt"
+	"reflect"
+	"sort"
+
+	"github.com/ipld/go-ipld-prime"
+)
+
+func Reflect(np ipld.NodePrototype, i interface{}) (ipld.Node, error) {
+	return defaultReflector.Reflect(np, i)
+}
+
+func ReflectIntoAssembler(na ipld.NodeAssembler, i interface{}) error {
+	return defaultReflector.ReflectIntoAssembler(na, i)
+}
+
+var defaultReflector = Reflector{
+	MapOrder: func(x, y string) bool {
+		return x < y
+	},
+}
+
+type Reflector struct {
+	// MapOrder is used to decide a deterministic order for inserting entries to maps.
+	// (This is used when converting golang maps, since their iteration order is randomized;
+	// it is not used when converting other types such as structs, since those have a stable order.)
+	// MapOrder should return x < y in the same way as sort.Interface.Less.
+	MapOrder func(x, y string) bool
+}
+
+func (rcfg Reflector) Reflect(np ipld.NodePrototype, i interface{}) (ipld.Node, error) {
+	nb := np.NewBuilder()
+	if err := rcfg.ReflectIntoAssembler(nb, i); err != nil {
+		return nil, err
+	}
+	return nb.Build(), nil
+}
+
+// ReflectIntoAssembler is a handy method for converting some basic golang types into Nodes.
+//
+// This plays fast and loose in general -- it's meant for demos and simple hacking, not for serious use.
+// For example, in reflecting on structs, Reflect assumes no anonymous fields or other complications.
+// There is no support for configuring converting struct fields with different names or other transformations.
+// And so forth.
+// If you need more control: this function is not what you should be using.
+func (rcfg Reflector) ReflectIntoAssembler(na ipld.NodeAssembler, i interface{}) error {
+	// Cover the most common values with a type-switch, as it's faster than reflection.
+	switch x := i.(type) {
+	case map[string]string:
+		keys := make([]string, 0, len(x))
+		for k := range x {
+			keys = append(keys, k)
+		}
+		sort.Sort(sortableStrings{keys, rcfg.MapOrder})
+		ma, err := na.BeginMap(len(x))
+		if err != nil {
+			return err
+		}
+		for _, k := range keys {
+			va, err := ma.AssembleEntry(k)
+			if err != nil {
+				return err
+			}
+			if err := va.AssignString(x[k]); err != nil {
+				return err
+			}
+		}
+		return ma.Finish()
+	case map[string]interface{}:
+		keys := make([]string, 0, len(x))
+		for k := range x {
+			keys = append(keys, k)
+		}
+		sort.Sort(sortableStrings{keys, rcfg.MapOrder})
+		ma, err := na.BeginMap(len(x))
+		if err != nil {
+			return err
+		}
+		for _, k := range keys {
+			va, err := ma.AssembleEntry(k)
+			if err != nil {
+				return err
+			}
+			if err := rcfg.ReflectIntoAssembler(va, x[k]); err != nil {
+				return err
+			}
+		}
+		return ma.Finish()
+	case []string:
+		la, err := na.BeginList(len(x))
+		if err != nil {
+			return err
+		}
+		for _, v := range x {
+			if err := la.AssembleValue().AssignString(v); err != nil {
+				return err
+			}
+		}
+		return la.Finish()
+	case []interface{}:
+		la, err := na.BeginList(len(x))
+		if err != nil {
+			return err
+		}
+		for _, v := range x {
+			if err := rcfg.ReflectIntoAssembler(la.AssembleValue(), v); err != nil {
+				return err
+			}
+		}
+		return la.Finish()
+	case string:
+		return na.AssignString(x)
+	case int:
+		return na.AssignInt(x)
+	case nil:
+		return na.AssignNull()
+	}
+	// That didn't fly?  Reflection time.
+	rv := reflect.ValueOf(i)
+	switch rv.Kind() {
+	case reflect.Bool:
+		return na.AssignBool(rv.Bool())
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		return na.AssignInt(int(rv.Int()))
+	case reflect.Float32, reflect.Float64:
+		return na.AssignFloat(rv.Float())
+	case reflect.String:
+		return na.AssignString(rv.String())
+	case reflect.Slice, reflect.Array:
+		l := rv.Len()
+		la, err := na.BeginList(l)
+		if err != nil {
+			return err
+		}
+		for i := 0; i < l; i++ {
+			if err := rcfg.ReflectIntoAssembler(la.AssembleValue(), rv.Index(i).Interface()); err != nil {
+				return err
+			}
+		}
+		return la.Finish()
+	case reflect.Map:
+		// the keys slice for sorting keeps things in reflect.Value form, because unboxing is cheap,
+		//  but re-boxing is not cheap, and the MapIndex method requires reflect.Value again later.
+		keys := make([]reflect.Value, 0, rv.Len())
+		itr := rv.MapRange()
+		for itr.Next() {
+			k := itr.Key()
+			if k.Kind() != reflect.String {
+				return fmt.Errorf("cannot convert a map with non-string keys (%T)", i)
+			}
+			keys = append(keys, k)
+		}
+		sort.Sort(sortableReflectStrings{keys, rcfg.MapOrder})
+		ma, err := na.BeginMap(rv.Len())
+		if err != nil {
+			return err
+		}
+		for _, k := range keys {
+			va, err := ma.AssembleEntry(k.String())
+			if err != nil {
+				return err
+			}
+			if err := rcfg.ReflectIntoAssembler(va, rv.MapIndex(k).Interface()); err != nil {
+				return err
+			}
+		}
+		return ma.Finish()
+	case reflect.Struct:
+		l := rv.NumField()
+		ma, err := na.BeginMap(l)
+		if err != nil {
+			return err
+		}
+		for i := 0; i < l; i++ {
+			fn := rv.Type().Field(i).Name
+			fv := rv.Field(i)
+			va, err := ma.AssembleEntry(fn)
+			if err != nil {
+				return err
+			}
+			if err := rcfg.ReflectIntoAssembler(va, fv.Interface()); err != nil {
+				return err
+			}
+		}
+		return ma.Finish()
+	case reflect.Ptr:
+		if rv.IsNil() {
+			return na.AssignNull()
+		}
+		return rcfg.ReflectIntoAssembler(na, rv.Elem())
+	case reflect.Interface:
+		return rcfg.ReflectIntoAssembler(na, rv.Elem())
+	}
+	// Some kints of values -- like Uintptr, Complex64/128, Channels, etc -- are not supported by this function.
+	return fmt.Errorf("fluent.Reflect: unsure how to handle type %T (kind: %v)", i, rv.Kind())
+}
+
+type sortableStrings struct {
+	a    []string
+	less func(x, y string) bool
+}
+
+func (a sortableStrings) Len() int           { return len(a.a) }
+func (a sortableStrings) Swap(i, j int)      { a.a[i], a.a[j] = a.a[j], a.a[i] }
+func (a sortableStrings) Less(i, j int) bool { return a.less(a.a[i], a.a[j]) }
+
+type sortableReflectStrings struct {
+	a    []reflect.Value
+	less func(x, y string) bool
+}
+
+func (a sortableReflectStrings) Len() int           { return len(a.a) }
+func (a sortableReflectStrings) Swap(i, j int)      { a.a[i], a.a[j] = a.a[j], a.a[i] }
+func (a sortableReflectStrings) Less(i, j int) bool { return a.less(a.a[i].String(), a.a[j].String()) }

fluent/reflect_test.go

+package fluent_test
+
+import (
+	"testing"
+
+	. "github.com/warpfork/go-wish"
+
+	ipld "github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/fluent"
+	"github.com/ipld/go-ipld-prime/must"
+	basicnode "github.com/ipld/go-ipld-prime/node/basic"
+)
+
+func TestReflect(t *testing.T) {
+	t.Run("Map", func(t *testing.T) {
+		n, err := fluent.Reflect(basicnode.Prototype.Any, map[string]interface{}{
+			"k1": "fine",
+			"k2": "super",
+			"k3": map[string]string{
+				"k31": "thanks",
+				"k32": "for",
+				"k33": "asking",
+			},
+		})
+		Wish(t, err, ShouldEqual, nil)
+		Wish(t, n.ReprKind(), ShouldEqual, ipld.ReprKind_Map)
+		t.Run("CorrectContents", func(t *testing.T) {
+			Wish(t, n.Length(), ShouldEqual, 3)
+			Wish(t, must.String(must.Node(n.LookupByString("k1"))), ShouldEqual, "fine")
+			Wish(t, must.String(must.Node(n.LookupByString("k2"))), ShouldEqual, "super")
+			n := must.Node(n.LookupByString("k3"))
+			Wish(t, n.Length(), ShouldEqual, 3)
+			Wish(t, must.String(must.Node(n.LookupByString("k31"))), ShouldEqual, "thanks")
+			Wish(t, must.String(must.Node(n.LookupByString("k32"))), ShouldEqual, "for")
+			Wish(t, must.String(must.Node(n.LookupByString("k33"))), ShouldEqual, "asking")
+		})
+		t.Run("CorrectOrder", func(t *testing.T) {
+			itr := n.MapIterator()
+			k, _, _ := itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k1")
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k2")
+			k, v, _ := itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k3")
+			itr = v.MapIterator()
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k31")
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k32")
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "k33")
+		})
+	})
+	t.Run("Struct", func(t *testing.T) {
+		type Woo struct {
+			A string
+			B string
+		}
+		type Whee struct {
+			X string
+			Z string
+			M Woo
+		}
+		n, err := fluent.Reflect(basicnode.Prototype.Any, Whee{
+			X: "fine",
+			Z: "super",
+			M: Woo{"thanks", "really"},
+		})
+		Wish(t, err, ShouldEqual, nil)
+		Wish(t, n.ReprKind(), ShouldEqual, ipld.ReprKind_Map)
+		t.Run("CorrectContents", func(t *testing.T) {
+			Wish(t, n.Length(), ShouldEqual, 3)
+			Wish(t, must.String(must.Node(n.LookupByString("X"))), ShouldEqual, "fine")
+			Wish(t, must.String(must.Node(n.LookupByString("Z"))), ShouldEqual, "super")
+			n := must.Node(n.LookupByString("M"))
+			Wish(t, n.Length(), ShouldEqual, 2)
+			Wish(t, must.String(must.Node(n.LookupByString("A"))), ShouldEqual, "thanks")
+			Wish(t, must.String(must.Node(n.LookupByString("B"))), ShouldEqual, "really")
+		})
+		t.Run("CorrectOrder", func(t *testing.T) {
+			itr := n.MapIterator()
+			k, _, _ := itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "X")
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "Z")
+			k, v, _ := itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "M")
+			itr = v.MapIterator()
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "A")
+			k, _, _ = itr.Next()
+			Wish(t, must.String(k), ShouldEqual, "B")
+		})
+	})
+	t.Run("NamedString", func(t *testing.T) {
+		type Foo string
+		type Bar struct {
+			Z Foo
+		}
+		n, err := fluent.Reflect(basicnode.Prototype.Any, Bar{"foo"})
+		Wish(t, err, ShouldEqual, nil)
+		Wish(t, n.ReprKind(), ShouldEqual, ipld.ReprKind_Map)
+		Wish(t, must.String(must.Node(n.LookupByString("Z"))), ShouldEqual, "foo")
+	})
+	t.Run("Interface", func(t *testing.T) {
+		type Zaz struct {
+			Z interface{}
+		}
+		n, err := fluent.Reflect(basicnode.Prototype.Any, Zaz{map[string]interface{}{"wow": "wee"}})
+		Wish(t, err, ShouldEqual, nil)
+		Wish(t, n.ReprKind(), ShouldEqual, ipld.ReprKind_Map)
+		n, err = n.LookupByString("Z")
+		Wish(t, err, ShouldEqual, nil)
+		Wish(t, n.ReprKind(), ShouldEqual, ipld.ReprKind_Map)
+		Wish(t, must.String(must.Node(n.LookupByString("wow"))), ShouldEqual, "wee")
+	})
+}