optimize filter ui (#736)

pkg/app/html-mount.new.txt

@@ -5,6 +5,6 @@
 goos: darwin
 goarch: arm64
 pkg: github.com/maxence-charriere/go-app/v9/pkg/app
-BenchmarkMountHTMLElement-10    	   52202	     23502 ns/op	  140310 B/op	      72 allocs/op
+BenchmarkMountHTMLElement-10    	   52926	     22826 ns/op	  140279 B/op	      71 allocs/op
 PASS
-ok  	github.com/maxence-charriere/go-app/v9/pkg/app	2.818s
+ok  	github.com/maxence-charriere/go-app/v9/pkg/app	2.692s

pkg/app/node.go

@@ -6,8 +6,6 @@ import (
 	"net/url"
 	"reflect"
 	"strings"
-
-	"github.com/maxence-charriere/go-app/v9/pkg/errors"
 )
 
 // UI is the interface that describes a user interface element such as
@@ -97,37 +95,44 @@ const (
 //
 // It should be used only when implementing components that can accept content
 // with variadic arguments like HTML elements Body method.
-func FilterUIElems(uis ...UI) []UI {
-	if len(uis) == 0 {
+func FilterUIElems(v ...UI) []UI {
+	if len(v) == 0 {
 		return nil
 	}
 
-	elems := make([]UI, 0, len(uis))
+	remove := func(i int) {
+		copy(v[i:], v[i+1:])
+		v[len(v)-1] = nil
+		v = v[:len(v)-1]
+	}
+
+	var b []UI
+	replaceAt := func(i int, s ...UI) {
+		b = append(b, v[i+1:]...)
+		v = append(v[:i], s...)
+		v = append(v, b...)
+		b = b[:0]
+	}
 
-	for _, n := range uis {
-		// Ignore nil elements:
-		if v := reflect.ValueOf(n); n == nil ||
-			v.Kind() == reflect.Ptr && v.IsNil() {
+	for i := len(v) - 1; i >= 0; i-- {
+		e := v[i]
+		if ev := reflect.ValueOf(e); e == nil || ev.Kind() == reflect.Pointer && ev.IsNil() {
+			remove(i)
 			continue
 		}
 
-		switch n.Kind() {
+		switch e.Kind() {
 		case SimpleText, HTML, Component, RawHTML:
-			elems = append(elems, n)
 
 		case Selector:
-			elems = append(elems, n.getChildren()...)
+			replaceAt(i, e.getChildren()...)
 
 		default:
-			panic(errors.New("filtering ui elements failed").
-				Tag("reason", "unexpected element type found").
-				Tag("kind", n.Kind()).
-				Tag("name", n.name()),
-			)
+			remove(i)
 		}
 	}
 
-	return elems
+	return v
 }
 
 func mount(d Dispatcher, n UI) error {

pkg/app/node_test.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -42,17 +43,37 @@ func TestKindString(t *testing.T) {
 
 func TestFilterUIElems(t *testing.T) {
 	var nilText *text
+	var foo *foo
 
 	simpleText := Text("hello")
 
 	expectedResult := []UI{
 		simpleText,
 	}
 
-	res := FilterUIElems(nil, nilText, simpleText)
+	res := FilterUIElems(nil, nilText, simpleText, foo)
 	require.Equal(t, expectedResult, res)
 }
 
+func BenchmarkFilterUIElems(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		FilterUIElems(Div().
+			Class("shell").
+			Body(
+				H1().Class("title").
+					Text("Hello"),
+				Input().
+					Type("text").
+					Class("in").
+					Value("World").
+					Placeholder("Type a name.").
+					OnChange(func(ctx Context, e Event) {
+						fmt.Println("Yo!")
+					}),
+			))
+	}
+}
+
 type mountTest struct {
 	scenario string
 	node     UI