【www.bbyears.com--设计基础】
golang不允许循环import package,如果检测到import cycle，会在编译时报错，通常import cycle是因为设计错误或包的规划问题。
以下面的例子为例，package a依赖package b，同事package b依赖package a
package a
import (
"fmt"
"github.com/mantishK/dep/b"
)
type A struct {
}
func (a A) PrintA() {
fmt.Println(a)
}
func NewA() *A {
a := new(A)
return a
}
func RequireB() {
o := b.NewB()
o.PrintB()
}
package b：
package b
import (
"fmt"
"github.com/mantishK/dep/a"
)
type B struct {
}
func (b B) PrintB() {
fmt.Println(b)
}
func NewB() *B {
b := new(B)
return b
}
func RequireA() {
o := a.NewA()
o.PrintA()
}
就会在编译时报错：
import cycle not allowed
package github.com/mantishK/dep/a
imports github.com/mantishK/dep/b
imports github.com/mantishK/dep/a
现在的问题就是：
A depends on B
B depends on A
那么如何避免？
引入package i， 引入interface
package i
type Aprinter interface {
PrintA()
}
让package b import package i
package b
import (
"fmt"
"github.com/mantishK/dep/i"
)
func RequireA(o i.Aprinter) {
o.PrintA()
}
引入package c
package c
import (
"github.com/mantishK/dep/a"
"github.com/mantishK/dep/b"
)
func PrintC() {
o := a.NewA()
b.RequireA(o)
}
现在依赖关系如下：
A depends on B
B depends on I
C depends on A and B