新增 Default 结构体和 SetDefault 方法

default.go

@@ -0,0 +1,37 @@
+package carbon
+
+var (
+	// default layout
+	// 默认布局模板
+	defaultLayout = DateTimeLayout
+
+	// default timezone
+	// 默认时区
+	defaultTimezone = Local
+
+	// default locale
+	// 默认区域
+	defaultLocale = "en"
+)
+
+// Default defines a Default struct.
+// 定义 Default 结构体
+type Default struct {
+	Layout   string
+	Timezone string
+	Locale   string
+}
+
+// SetDefault sets default.
+// 设置全局默认值
+func SetDefault(d Default) {
+	if d.Layout != "" {
+		defaultLayout = d.Layout
+	}
+	if d.Timezone != "" {
+		defaultTimezone = d.Timezone
+	}
+	if d.Locale != "" {
+		defaultLocale = d.Locale
+	}
+}

default_bench_test.go

@@ -0,0 +1,14 @@
+package carbon
+
+import "testing"
+
+func BenchmarkCarbon_SetDefault(b *testing.B) {
+	d := Default{
+		Layout:   DateTimeLayout,
+		Timezone: Local,
+		Locale:   "en",
+	}
+	for n := 0; n < b.N; n++ {
+		SetDefault(d)
+	}
+}

default_unit_test.go

@@ -0,0 +1,17 @@
+package carbon
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestCarbon_SetDefault(t *testing.T) {
+	SetDefault(Default{
+		Layout:   DateTimeLayout,
+		Timezone: Local,
+		Locale:   "en",
+	})
+	assert.Equal(t, DateTimeLayout, defaultLayout)
+	assert.Equal(t, Local, defaultTimezone)
+	assert.Equal(t, "en", defaultLocale)
+}