检查Go中的nil和nil接口

Question

目前我正在使用这个辅助函数来检查nil和nil接口

func isNil(a interface{}) bool {
  defer func() { recover() }()
  return a == nil || reflect.ValueOf(a).IsNil()
}

由于reflect.ValueOf(a).IsNil()恐慌,如果该值的种类比其他任何东西Chan,Func,Map,Ptr,Interface或者Slice,我在推迟扔recover()赶上那些.

有没有更好的方法来实现这项检查？它认为应该有一个更直接的方式来做到这一点.

Answer 1

在golang-nuts邮件列表中查看Kyle在此主题中的答案.

简而言之:如果您从未存储(*T)(nil)在界面中,那么您可以可靠地使用与nil的比较,而无需使用反射.另一方面,为接口分配无类型的nil总是正常的.

Answer 2

如果以前的选项都不适合你,那么到目前为止我能做到的最好的是:

if c == nil || (reflect.ValueOf(c).Kind() == reflect.Ptr && reflect.ValueOf(c).IsNil())

至少它检测到(*T)(无)的情况.

Answer 3

Two solutions NOT using reflection:

Copy and paste code into editor at: https://play.golang.org/ to see in action.

1: Add an "IsInterfaceNil()" function to interface.

2: Use A "type switch"

CODE BELOW:

????????????????????

EXAMPLE #1: IsInterfaceNil()

????????????????????

//:Example #1:
//:I prefer this method because the 
//:TakesInterface function does NOT need to know
//:about all the different implementations of
//:the interface.
package main;
import "fmt";

func main()(){

    var OBJ_OK *MyStruct = &( MyStruct{} );
    var NOT_OK *MyStruct = nil;

    //:Will succeed:
    TakesInterface( OBJ_OK );

    //:Will fail:
    TakesInterface( NOT_OK );

}

func TakesInterface( input_arg MyInterface ){

    if( input_arg.IsInterfaceNil() ){
        panic("[InputtedInterfaceIsNil]");
    }

    input_arg.DoThing();
}

type MyInterface interface{
    DoThing()()
    IsInterfaceNil()(bool)
}
type MyStruct struct{}
func(f *MyStruct)DoThing()(){
    fmt.Println("[MyStruct.DoThing]");
}
func(f *MyStruct)IsInterfaceNil()(bool){
    if(nil==f){ return true; }
    return false;
}

????????????????????

EXAMPLE #2: Type Switch

????????????????????

//:Example #2:
//:This will also work, but the function taking
//:the interface needs to know about all 
//:implementations. This defeats a bit of the
//:decoupling from implementation that an
//:interface offers, but if you are just using
//:interfaces for polymorphism, it's probably
//:an okay way to go. (opinion)
package main;
import "fmt";

func main()(){

    //:Will succeed:
    var OBJ_OK *IMPLMENTS_INTERFACE_01 = 
             &( IMPLMENTS_INTERFACE_01{} );
    TakesInterface( OBJ_OK );

    //:Will fail:
    var NOT_OK *IMPLMENTS_INTERFACE_01 = nil;
    TakesInterface( NOT_OK );
}

func TakesInterface( hasDoThing MyInterface ){

    //:THIS WILL NOT WORK:
    if(nil==hasDoThing){
        panic("[This_Error_Message_Will_Never_Happen]");
    }

    //:TYPE SWITCH TO THE RESCUE:
    switch v := hasDoThing.(type){

        case (*IMPLMENTS_INTERFACE_01): 
        if(nil==v){ panic("[Nil_PTR_01]"); }

        case (*IMPLMENTS_INTERFACE_02): 
        if(nil==v){ panic("[Nil_PTR_02]"); }

        case (*IMPLMENTS_INTERFACE_03): 
        if(nil==v){ panic("[Nil_PTR_03]"); }

        default: 
            panic("[UnsupportedInterface]");
    }

    hasDoThing.DoThing();

}

type IMPLMENTS_INTERFACE_01 struct{};
type IMPLMENTS_INTERFACE_02 struct{};
type IMPLMENTS_INTERFACE_03 struct{};
func (f *IMPLMENTS_INTERFACE_01)DoThing()(){
    fmt.Println( "DoingTheThing_01" );
}
func (f *IMPLMENTS_INTERFACE_02)DoThing()(){
    fmt.Println( "DoingTheThing_02" );
}
func (f *IMPLMENTS_INTERFACE_03)DoThing()(){
    fmt.Println( "DoingTheThing_03" );
}

type MyInterface interface{
    DoThing()()
}

UPDATE: After implementing in my code base, I found #2 (type switch) to be best solution. Specifically because I DON'T want to EDIT the glfw.Window struct in the bindings library I am using. Here is a paste-bin of my use-case. Apologies for my non-standard coding style. https://pastebin.com/22SUDeGG