Golang学习笔记_21——Reader
Golang学习笔记_22——Reader示例
Golang学习笔记_23——error补充

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泛型

Go语言从1.18版本开始引入了泛型，这是Go语言的一个重要特性，它允许函数、类型和接口在定义时不必绑定到特定的类型上，而是可以在后续使用时再指定具体的类型。这极大地增强了代码的复用性和灵活性。

1. 泛型中的类型参数

类型参数是泛型函数、泛型类型和泛型接口定义中声明的占位符，它们用于表示在泛型实例化时可以指定的具体类型。

1.1 类型参数声明

在泛型定义中，类型参数通过方括号[]中的类型参数列表进行声明。

func Print[T any](x T) {...}
type Pair[T, U any] struct {...}
type Describer[T any] interface {...}

1.2 类型参数的约束

类型参数可以受到约束，这意味着它们必须满足特定的接口。这通过类型约束来实现。

// Generics type constraints
type Number interface {int | int64 | float64 // 使用联合类型表示约束
}func Sum[T Number](nums []T) T {var sum Tfor _, num := range nums {sum += num}return sum
}

测试方法

func TestSum(t *testing.T) {type args[T Number] struct {nums []T}type testCase[T Number] struct {name stringargs args[T]want T}intTests := []testCase[int]{{name: "int add",args: args[int]{nums: []int{1, 2, 3},},want: 6,},}floatTests := []testCase[float64]{{name: "float add",args: args[float64]{nums: []float64{1.1, 2.2, 3.3},},want: 6.6,},}strTests := []testCase[string]{{name: "string add",args: args[string]{nums: []string{"1", "2", "3"},},want: "123",},}for _, tt := range strTests {t.Run(tt.name, func(t *testing.T) {if got := Sum(tt.args.nums); got != tt.want {t.Errorf("Sum() = %v, want %v", got, tt.want)}})}for _, tt := range intTests {t.Run(tt.name, func(t *testing.T) {if got := Sum(tt.args.nums); got != tt.want {t.Errorf("Sum() = %v, want %v", got, tt.want)}})}for _, tt := range floatTests {t.Run(tt.name, func(t *testing.T) {if got := Sum(tt.args.nums); got != tt.want {t.Errorf("Sum() = %v, want %v", got, tt.want)}})}}

输出结果

strTests 测试结果
# Golang/generics_demo [Golang/generics_demo.test]
./generics_demo_test.go:37:25: string does not satisfy Number (string missing in int | int64 | float64)
./generics_demo_test.go:40:15: string does not satisfy Number (string missing in int | int64 | float64)
./generics_demo_test.go:48:17: string does not satisfy Number (string missing in int | int64 | float64)intTests floatTests 测试结果
=== RUN   TestSum
=== RUN   TestSum/int_add
=== RUN   TestSum/float_add
--- PASS: TestSum (0.00s)--- PASS: TestSum/int_add (0.00s)--- PASS: TestSum/float_add (0.00s)
PASS

1.3 类型参数的实例化

在调用泛型函数、创建泛型类型的实例或赋值给泛型接口时，类型参数会被具体化（实例化）。这可以显式地通过类型参数列表进行，也可以由编译器自动推断。

Print[int](42)           // 显式指定T为int类型
Print(3.14)              // 编译器自动推断T为float64类型
var p Pair[int, string]  // 显式指定T为int，U为string类型

2. 泛型函数

泛型函数允许在函数签名中声明类型参数，这些参数将在函数调用时具体化。

func genericFuncDemo[T any](value T) {fmt.Println(value)
}func testGenericFuncDemo() {genericFuncDemo(1)genericFuncDemo("hello")genericFuncDemo(1.1)
}

测试方法

=== RUN   Test_testGenericFuncDemo
1
hello
1.1
--- PASS: Test_testGenericFuncDemo (0.00s)
PASS

3. 泛型类型

type Pair[T, U any] struct {First  TSecond U
}func PairDemo() {pair := Pair[int, string]{First: 10, Second: "hello"}fmt.Println(pair.First, pair.Second)
}

测试方法

func TestPairDemo(t *testing.T) {PairDemo()
}

输出结果

=== RUN   TestPairDemo
10 hello
--- PASS: TestPairDemo (0.00s)
PASS

4. 泛型接口

// generics interface
type Describer[T any] interface {Describe(T) string
}type IntDescriber struct {
}func (num IntDescriber) Describe(i int) string {return fmt.Sprintf("类型是：%d", i)
}func DescribeDemo() {var test Describer[int]test = IntDescriber{}fmt.Println(test.Describe(100))
}

测试方法

func TestDescribeDemo(t *testing.T) {DescribeDemo()
}

输出结果

=== RUN   TestDescribeDemo
类型是：100
--- PASS: TestDescribeDemo (0.00s)
PASS

源码

// generics_demo.go 文件
package generics_demoimport "fmt"// Generics type constraints
type Number interface {int | int64 | float64 // 使用联合类型表示约束
}func Sum[T Number](nums []T) T {var sum Tfor _, num := range nums {sum += num}return sum
}func genericFuncDemo[T any](value T) {fmt.Println(value)
}func testGenericFuncDemo() {genericFuncDemo(1)genericFuncDemo("hello")genericFuncDemo(1.1)
}type Pair[T, U any] struct {First  TSecond U
}func PairDemo() {pair := Pair[int, string]{First: 10, Second: "hello"}fmt.Println(pair.First, pair.Second)
}// generics interface
type Describer[T any] interface {Describe(T) string
}type IntDescriber struct {
}func (num IntDescriber) Describe(i int) string {return fmt.Sprintf("类型是：%d", i)
}func DescribeDemo() {var test Describer[int]test = IntDescriber{}fmt.Println(test.Describe(100))
}

// generics_demo_test.go 文件
package generics_demoimport ("testing"
)func TestSum(t *testing.T) {type args[T Number] struct {nums []T}type testCase[T Number] struct {name stringargs args[T]want T}intTests := []testCase[int]{{name: "int add",args: args[int]{nums: []int{1, 2, 3},},want: 6,},}floatTests := []testCase[float64]{{name: "float add",args: args[float64]{nums: []float64{1.1, 2.2, 3.3},},want: 6.6,},}//strTests := []testCase[string]{//	{//		name: "string add",//		args: args[string]{//			nums: []string{"1", "2", "3"},//		},//		want: "123",//	},//}//for _, tt := range strTests {//	t.Run(tt.name, func(t *testing.T) {//		if got := Sum(tt.args.nums); got != tt.want {//			t.Errorf("Sum() = %v, want %v", got, tt.want)//		}//	})//}for _, tt := range intTests {t.Run(tt.name, func(t *testing.T) {if got := Sum(tt.args.nums); got != tt.want {t.Errorf("Sum() = %v, want %v", got, tt.want)}})}for _, tt := range floatTests {t.Run(tt.name, func(t *testing.T) {if got := Sum(tt.args.nums); got != tt.want {t.Errorf("Sum() = %v, want %v", got, tt.want)}})}}func Test_testGenericFuncDemo(t *testing.T) {testGenericFuncDemo()
}func TestPairDemo(t *testing.T) {PairDemo()
}func TestDescribeDemo(t *testing.T) {DescribeDemo()
}