diff --git a/cache_test.go b/cache_test.go
index c1a4d80..904a2df 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -198,21 +198,22 @@ func TestFlush(t *testing.T) {
 }
 
 func TestOnEvicted(t *testing.T) {
-	tc := New_tpl(Attr_tpl{
+	works := false
+	var tc *Cache_tpl
+	tc = New_tpl(Attr_tpl{
 		DefaultExpiration:      DefaultExpiration,
 		DefaultCleanupInterval: 0,
+		OnEvicted: func(k string, v ValueType_tpl) {
+			if k == "foo" && v == 3 {
+				works = true
+			}
+			tc.Set("bar", 4, DefaultExpiration)
+		},
 	})
 	tc.Set("foo", 3, DefaultExpiration)
-	if tc.onEvicted != nil {
-		t.Fatal("tc.onEvicted is not nil")
+	if tc.onEvicted == nil {
+		t.Fatal("tc.onEvicted is nil")
 	}
-	works := false
-	tc.OnEvicted(func(k string, v ValueType_tpl) {
-		if k == "foo" && v == 3 {
-			works = true
-		}
-		tc.Set("bar", 4, DefaultExpiration)
-	})
 	tc.Delete("foo")
 	x, _ := tc.Get("bar")
 	if !works {
diff --git a/cachemap/cache.tmpl b/cachemap/cache.tmpl
index 26dc373..351c3c0 100644
--- a/cachemap/cache.tmpl
+++ b/cachemap/cache.tmpl
@@ -182,8 +182,7 @@ func (c *cache) delete(k string) ({{.ValueType}}, bool) {
 		delete(c.items, k)
 		return v.Object, true
 	}
-	//TODO: zeroValue
-	return 0, false
+	return {{ .ZeroValue }}, false
 }
 
 func (c *cache) deleteFast(k string) {
diff --git a/cachemap/main.go b/cachemap/main.go
index 3c2dd4e..e7f480d 100644
--- a/cachemap/main.go
+++ b/cachemap/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"go/ast"
 	"go/parser"
 	"go/token"
 	"os"
@@ -25,6 +26,61 @@ func packageDir() string {
 	return path.Dir(filename)
 }
 
+// find value of ident 'grammar' in GenDecl.
+func findInGenDecl(genDecl *ast.GenDecl, grammarName string) string {
+	for _, spec := range genDecl.Specs {
+		valueSpec, ok := spec.(*ast.TypeSpec)
+		if ok {
+			// type ident
+			ident, ok := valueSpec.Type.(*ast.Ident)
+			if ok {
+				return ident.Name
+			}
+		}
+	}
+	return ""
+}
+
+func findInDecl(decl ast.Decl, grammarName string) string {
+	genDecl, ok := decl.(*ast.GenDecl)
+	if ok {
+		g := findInGenDecl(genDecl, grammarName)
+		if g != "" {
+			return g
+		}
+	}
+	return ""
+}
+
+// zeroValue returns literal zero value.
+func zeroValue(s string) string {
+	// TODO: support func type.
+	switch s {
+	case "string":
+		return "\"\""
+	case "int", "uint", "int64", "uint64", "uint32", "int32", "int16",
+		"uint16", "int8", "uint8", "byte", "rune", "float64", "float32",
+		"complex64", "complex32", "uintptr":
+		return "0"
+	case "slice":
+		return "nil"
+	default:
+		if s[0] == '*' { // Pointer
+			return "nil"
+		}
+		return s + "{}"
+	}
+}
+
+// TODO: support more builtin types
+func builtin(s string) bool {
+	switch s {
+	case "string":
+		return true
+	}
+	return false
+}
+
 func main() {
 	keyType := flag.String("k", "", "key type")
 	valueType := flag.String("v", "", "value type")
@@ -40,10 +96,23 @@ func main() {
 	if err != nil {
 		fatal(err)
 	}
-	var packageName string
-	for name := range pkgs {
+	packageName := "main"
+	typeName := ""
+	for name, pkg := range pkgs {
 		packageName = name
+		for _, f := range pkg.Files {
+			for _, decl := range f.Decls {
+				typeName = findInDecl(decl, *valueType)
+			}
+		}
 	}
+	if typeName == "" && !builtin(*valueType) {
+		fatal(fmt.Errorf("found no definition of %s in files\n", *valueType))
+	}
+	if typeName == "" {
+		typeName = *valueType
+	}
+	zeroTypeValue := zeroValue(typeName)
 	f, err := os.OpenFile(fmt.Sprintf("%s2%s_cachemap.go", *keyType, *valueType), os.O_TRUNC|os.O_WRONLY|os.O_CREATE, 0644)
 	if err != nil {
 		fatal(err)
@@ -59,6 +128,7 @@ func main() {
 			"ValueType":   *valueType,
 			"PackageName": packageName,
 			"Cache":       fmt.Sprintf("String2%sCache", *valueType),
+			"ZeroValue":   zeroTypeValue,
 		},
 	)
 	if err != nil {