go一些技巧

Signed-off-by: kaisawind <wind.kaisa@gmail.com>

source/_posts/2020-06-15-go.md

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+---
+layout: post
+title:  "go一些技巧"
+date: 2020-06-15 09:21:12 +0800
+categories: [golang]
+excerpt_separator: <!--more-->
+---
+go一些技巧
+<!--more-->
+
+1. map第二个返回值
+go语言的map有第二个返回值，能够判断在map中key是否存在
+```go
+value, ok := kv[key]
+if !ok {
+    // do something
+}
+```
+
+2. `_`无视其中一个值
+使用`_`可以无视多个值中的其中几个或全部
+```go
+_, ok := kv[key]
+if !ok {
+    // do something
+}
+```
+无视全部值
+```go
+_, _ := kv[key]
+```
+
+3. 在切片后追加元素
+```go
+var arr []int
+arr = append(arr, 1)
+```
+
+
+4. 在切片前追加元素
+```go
+var arr []int
+arr = append([]int{1}, arr...)
+```
+
+5. 在切片后追加多个元素
+```go
+var arr []int
+arr = append(arr, []int{1, 2, 3, 4, 5}...)
+```
+
+6. 切片越界
+
+不会越界，是空切片
+```go
+fmt.Println(arr[len(arr):])
+```
+
+会越界
+```go
+fmt.Println(arr[len(arr)+1:])
+```
+
+会越界
+```go
+fmt.Println(arr[len(arr)])
+```
+
+7. 弃用标记
+```go
+// Execer is an optional interface that may be implemented by a Conn.
+//
+// If a Conn does not implement Execer, the sql package's DB.Exec will
+// first prepare a query, execute the statement, and then close the
+// statement.
+//
+// Exec may return ErrSkip.
+//
+// Deprecated: Drivers should implement ExecerContext instead (or additionally).
+type Execer interface {
+	Exec(query string, args []Value) (Result, error)
+}
+```
+
+8. BUG标记
+```go
+// BUG(who): 我是bug说明
+```
+
+9. 包注释
+单独doc.go文件
+```go
+package aaa
+
+// Execer is an optional interface that may be implemented by a Conn.
+//
+// If a Conn does not implement Execer, the sql package's DB.Exec will
+// first prepare a query, execute the statement, and then close the
+// statement.
+//
+// Exec may return ErrSkip.
+```
+
+10. Example
+文件名`example_xxx_test.go`
+包名`xxx_test`
+函数名`func Example[FuncName][_tag]()`
+函数尾 `// Output:`
+```go
+// 文件必须放在 banana包目录下, 名字必须为example_xxx_test.go
+
+// Package banana_test 为banana包的示例
+package banana_test
+
+// 此注释将会被展示在页面上
+// 此函数将被展示在OverView区域
+func Example() {
+    fmt.Println("Hello OverView")
+
+    // Output:
+    // Hello OverView
+}
+```
+
+11. UnitTest
+
+文件名`xxx_test.go`
+包名`xxx_test`
+函数名`func Test[FuncName][_tag]()`
+
+```go
+package server_test
+
+import (
+	"testing"
+    "time"
+)
+func TestServerTimeLayout1(t *testing.T) {
+	some := time.Now().Format(types.TimeLayout1)
+	t.Log(some)
+}
+```
+
+12. BenchmarkTest
+文件名`xxx_test.go`
+包名`xxx_test`
+函数名`func Benchmark[FuncName][_tag]()`
+
+```go
+package types_test
+
+func BenchmarkDataMarshal(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		data := Data{
+			MsgType: DeviceReq,
+			Data: []*DeviceS{
+				{
+					DeviceID:  "abc-123_&%S",
+					ServiceID: "discrete",
+					EventTime: "123456",
+					Data: map[string]interface{}{
+						"LD_14.XY": "0",
+						"LD_15.XY": 0,
+						"LD_16.XY": int64(64),
+						"LD_17.XY": true,
+						"LD_18.XY": 123.456,
+					},
+				},
+			},
+		}
+		_, err := json.Marshal(data)
+		if err != nil {
+			b.FailNow()
+		}
+		// fmt.Println("json", string(bytes))
+	}
+
+}
+```