英文:
interface & integer comparison in golang
问题
我不明白为什么第一个结果是false而第二个结果是true。
任何帮助将不胜感激。
func main() {
var i interface{}
i = uint64(0)
fmt.Println("[1] ", reflect.TypeOf(i), i == 0)
i = 0
fmt.Println("[2] ", reflect.TypeOf(i), i == 0)
var n uint64 = 32
fmt.Println("[3] ", reflect.TypeOf(n), n == 32)
}
// 结果
// [1] uint64 false
// [2] int true
// [3] uint64 true
在这里尝试 Go playground
英文:
I don't understand why the first result is false while second is true.
Any help will be appreciated.
func main() {
var i interface{}
i = uint64(0)
fmt.Println("[1] ", reflect.TypeOf(i), i == 0)
i = 0
fmt.Println("[2] ", reflect.TypeOf(i), i == 0)
var n uint64 = 32
fmt.Println("[3] ", reflect.TypeOf(n), n == 32)
}
// result
// [1] uint64 false
// [2] int true
// [3] uint64 true
Try it here Go playground
答案1
得分: 11
因为0
是一个未指定类型的常量,默认类型是int
,而不是uint64
。当与接口进行比较时,你所比较的对象必须既是相同类型又是相同值才被认为是相等的。
参考链接:https://golang.org/ref/spec#Comparison_operators
等号操作符
==
和!=
适用于可比较的操作数。小于号<
、小于等于号<=
、大于号>
和大于等于号>=
适用于有序的操作数。这些术语和比较的结果定义如下:非接口类型X的值x和接口类型T的值t是可比较的,当X的值是可比较的并且X实现了T时。如果t的动态类型与X相同且t的动态值等于x,则它们是相等的。
英文:
Because 0
is an untyped constant whose default type is int
, not uint64
, and when doing comparison with an interface, the thing you are comparing to must be both the same type and the same value for them to be considered equal.
https://golang.org/ref/spec#Comparison_operators
> The equality operators == and != apply to operands that are comparable. The ordering operators <, <=, >, and >= apply to operands that are ordered. These terms and the result of the comparisons are defined as follows:
>
> A value x of non-interface type X and a value t of interface type T are comparable when values of type X are comparable and X implements T. They are equal if t's dynamic type is identical to X and t's dynamic value is equal to x.
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