英文:
go type-switch how to deal with point to nil
问题
像这样，如果msg指向null值，如何在clean code中处理它？
func test(a SomeType) {
switch msg := a.(type) {
case *type1:
dosomething1(a)
case *type2:
dosomething2(a)
case *type3:
dosomething3(a)
default:
do()
}
}
主函数可能是这样的：
func main() {
var b_ptr *stTest
aa := interface{}(b)
test(aa)
}
type test struct {
c int
d string
}
b_ptr是一个指针，但它指向nil，我想在test函数中判断它。如果我在test函数中使用b_ptr，例如打印a.c或a.d，程序会崩溃。
我通过以下方式解决了这个问题。在每个case中使用if语句，检查msg是否为nil，但这样做太愚蠢了。
func test(a SomeType) {
switch msg := a.(type) {
case *type1:
if msg == nil {
return
}
dosomething1(a)
case *type2:
if msg == nil {
return
}
dosomething2(a)
case *type3:
if msg == nil {
return
}
dosomething3(a)
default:
do()
}
}
英文:
like this, if msg point to null value, how to deal with it in clean code
func test(a SomeType) {
switch msg := a.(type) {
case *type1:
dosomething1(a)
case *type2:
dosomething2(a)
case *type3:
dosomething3(a)
default:
do()
}
the main func may be this
func main() {
var b_ptr *stTest
aa := interface{}(b)
test(aa)
}
type test struct {
c int
d string
}
b_ptr is a pointer, but it point to nil, i want to judge it in test func
if i use b_ptr in test func, eg: print a.c or a.d, it will crash.
i do it by this way. do if(), everywhere use a, but it too stupid.
func test(a SomeType) {
switch msg := a.(type) {
case *type1:
if msg == nil {
return
}
dosomething1(a)
case *type2:
if msg == nil {
return
}
dosomething2(a)
case *type3:
if msg == nil {
return
}
dosomething3(a)
default:
do()
}
答案1
得分: 1
通常情况下，这应该被视为调用者的问题，因此处理后果应该是调用者的责任。传递非nil值的接口是一种不好的做法，除非这是有意为之的。
然而，如果你无法避免使用非nil指针的接口，你可以使用reflect来检查底层值是否为nil。
func test(a SomeType) {
if rv := reflect.ValueOf(a); !rv.IsValid() || rv.IsNil() {
return
}
switch msg := a.(type) {
case *type1:
dosomething1(a)
case *type2:
dosomething2(a)
case *type3:
dosomething3(a)
default:
do()
}
}
英文:
Generally this ought to be considered a problem with the caller, and therefore it should be the caller's job to deal with the fallout. Passing around non-nil interfaces that hold nil values is bad practice unless it's intentional/expected.
If you can't avoid the non-nil interface with nil-pointer however, then you can use reflect to check if the underlying value is nil.
func test(a SomeType) {
if rv := reflect.ValueOf(a); !rv.IsValid() || rv.IsNil() {
return
}
switch msg := a.(type) {
case *type1:
dosomething1(a)
case *type2:
dosomething2(a)
case *type3:
dosomething3(a)
default:
do()
}
}
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