Add X() to new builder (#66)

README.md

@@ -151,7 +151,7 @@ func main() {
                 sb.Select("id","type").From("t_pet").Gt("id", 10000) //....
             }
 
-        builder := Of(nil).
+        builder := X().
 		Select("p.id","p.weight").
 		FromX(func(fb *FromBuilder) {
                     fb.

builder_x.go

@@ -38,9 +38,7 @@ type BuilderX struct {
 }
 
 func Of(tableNameOrPo interface{}) *BuilderX {
-	x := new(BuilderX)
-	x.bbs = []Bb{}
-	x.sxs = []*FromX{}
+	x := X()
 	if tableNameOrPo != nil {
 		switch tableNameOrPo.(type) {
 		case string:
@@ -52,6 +50,13 @@ func Of(tableNameOrPo interface{}) *BuilderX {
 	return x
 }
 
+func X() *BuilderX {
+	x := new(BuilderX)
+	x.bbs = []Bb{}
+	x.sxs = []*FromX{}
+	return x
+}
+
 func (x *BuilderX) FromX(fromX func(fb *FromBuilder)) *BuilderX {
 
 	if len(x.sxs) == 0 {

cond_builder.go

@@ -255,7 +255,7 @@ func (cb *CondBuilder) NonNull(key string) *CondBuilder {
 
 func (cb *CondBuilder) X(k string, vs ...interface{}) *CondBuilder {
 	bb := Bb{
-		op:    X,
+		op:    XX,
 		key:   k,
 		value: vs,
 	}

oper.go

@@ -17,7 +17,7 @@
 package sqlxb
 
 const (
-	X        = ""
+	XX       = ""
 	AGG      = ""
 	SUB      = "SUB"
 	AND      = "AND"

to_sql.go

@@ -76,7 +76,7 @@ func (built *Built) toFromSql(vs *[]interface{}, bp *strings.Builder) {
 func (built *Built) toBb(bb Bb, bp *strings.Builder, vs *[]interface{}) {
 	op := bb.op
 	switch op {
-	case X:
+	case XX:
 		bp.WriteString(bb.key)
 		if vs != nil && bb.value != nil {
 			arr := bb.value.([]interface{})