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inject.go
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inject.go
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package do
import (
"fmt"
"log"
"reflect"
"unsafe"
)
// Ioc 控制反转,Inversion of Control
type Ioc struct {
enableUnexportedFieldSetValue bool // 开启对非导出字段的赋值
print bool
providerMap map[reflect.Type]typeInfo
cache map[reflect.Type]reflect.Value
}
type IocOption struct {
EnableUnexportedFieldSetValue bool // 开启对非导出字段的赋值
Print bool // 打印初始话的对象
}
type typeInfo struct {
depType []reflect.Type
provider reflect.Value
}
func NewIoc(
opt *IocOption,
) *Ioc {
if opt == nil {
opt = &IocOption{}
}
return &Ioc{
enableUnexportedFieldSetValue: opt.EnableUnexportedFieldSetValue,
print: opt.Print,
providerMap: make(map[reflect.Type]typeInfo),
cache: make(map[reflect.Type]reflect.Value),
}
}
// RegisterProvider 注册provider函数,形如`func New(fielda TypeA, fieldb TypeB) (T)`
func (ioc *Ioc) RegisterProvider(v any) (err error) {
refValue := reflect.ValueOf(v)
refType := refValue.Type()
if refType.Kind() != reflect.Func {
return fmt.Errorf("please input func")
}
// 分析函数的参数和返回值
ti := typeInfo{
depType: make([]reflect.Type, 0, refType.NumIn()),
provider: refValue,
}
for i := 0; i < refType.NumIn(); i++ {
in := refType.In(i)
ti.depType = append(ti.depType, in)
}
// 返回:instance
min := 1
if refType.NumOut() == 0 {
return fmt.Errorf("can't find result in func")
}
if refType.NumOut() < min {
return fmt.Errorf("too little result in func, min is %d", min)
}
for i := 0; i < refType.NumOut(); i++ {
out := refType.Out(i)
ioc.providerMap[out] = ti
}
return
}
// Inject 为对象注入依赖,传入结构体指针,根据结构体的字段类型找到对应的provider,执行后将获得的值赋予字段
//
// 如果provider需要参数,则根据参数类型继续找寻相应的provider,直至初始化完成
func (ioc *Ioc) Inject(v any) (err error) {
refValue := reflect.ValueOf(v)
refType := refValue.Type()
if refType.Kind() != reflect.Ptr {
return fmt.Errorf("v is not a pointer")
}
eleValue := refValue.Elem()
eleType := eleValue.Type()
if eleType.Kind() != reflect.Struct {
return fmt.Errorf("v is not a struct")
}
ioc.levelPrint(0, "will inject object of type(%s)\n", eleType.Name())
// 遍历field
for i := 0; i < eleValue.NumField(); i++ {
sf := eleType.Field(i)
field := eleValue.Field(i)
fieldType := field.Type()
var level = 1
ioc.levelPrint(level, "will set field %s(%s)\n", sf.Name, fieldType.Name())
// 根据类型查找值
var value reflect.Value
value, err = ioc.find(fieldType, level+1)
if err != nil {
return
}
// 给字段赋值
if ioc.enableUnexportedFieldSetValue {
rf := reflect.NewAt(field.Type(), unsafe.Pointer(field.UnsafeAddr())).Elem()
rf.Set(value)
} else {
field.Set(value)
}
ioc.levelPrint(level, "finish set field %s(%s)\n", sf.Name, fieldType.Name())
}
ioc.levelPrint(0, "finish inject object of type(%s)\n", eleType.Name())
return
}
func (ioc *Ioc) levelPrint(l int, format string, args ...any) {
if ioc.print {
prefix := "[inject] "
level := ""
for i := 0; i < l; i++ {
level += " "
}
log.Printf(prefix+level+format, args...)
}
}
var (
emptyStruct = reflect.TypeOf((*struct{})(nil))
emptyStructValue = reflect.New(emptyStruct.Elem()).Elem()
emptyStructPtrValue = reflect.New(emptyStruct).Elem()
errorType = reflect.TypeOf((*error)(nil)).Elem()
)
func (ioc *Ioc) find(typ reflect.Type, level int) (r reflect.Value, err error) {
ioc.levelPrint(level, "will get field type %s's value\n", typ.Name())
value, ok := ioc.cache[typ]
if ok {
ioc.levelPrint(level, "finish get field type %s's value from cache\n", typ.Name())
return value, nil
}
// 在provider里寻找初始化函数
provider, ok := ioc.providerMap[typ]
if !ok {
// 检查类型是否是struct{}
if typ.ConvertibleTo(emptyStruct.Elem()) {
ioc.levelPrint(level, "finish get field type %s's value from empty struct\n", typ.Name())
return emptyStructValue, nil
}
if typ.ConvertibleTo(emptyStruct) {
ioc.levelPrint(level, "finish get field type %s's value from empty struct pointer\n", typ.Name())
return emptyStructPtrValue, nil
}
return r, fmt.Errorf("can't find provider of %+v", typ)
}
// 调用
in := make([]reflect.Value, 0, len(provider.depType))
for _, dep := range provider.depType {
// 在已有provider里找指定类型
var value reflect.Value
if value, ok = ioc.cache[dep]; !ok {
value, err = ioc.find(dep, level+1)
if err != nil {
return r, err
}
ioc.cache[dep] = value
}
in = append(in, value)
}
newValues := provider.provider.Call(in)
if len(newValues) == 0 {
return r, fmt.Errorf("can't get new value by provider")
}
// 返回值里,第一个必须是实例,最后一个必须是error,中间的忽略
newValue := newValues[0]
ioc.cache[typ] = newValue
if len(newValues) > 1 {
lastValue := newValues[len(newValues)-1]
last := lastValue.Interface()
if lastValue.Type().Implements(errorType) {
if v, ok := last.(error); ok {
if v != nil {
return r, fmt.Errorf("call failed, err is %+v", v)
}
}
} else {
return r, fmt.Errorf("last return value is not error, is %+v", last)
}
}
ioc.levelPrint(level, "finish get field type %s's value from provider `%s`\n", typ.Name(), provider.provider.Type().String())
return newValue, nil
}