英文:
Why does golang allow named slice type assignment without explicit type conversion?
问题
我以为Go语言不允许在没有显式类型转换的情况下将命名类型赋值给实际类型。
但是如果我将[]byte赋值给json.RawMessage，它为什么可以编译通过而没有错误呢？
var a json.RawMessage // 类型 RawMessage []byte
var b []byte
a = b
var x time.Duration // 类型 Duration int64
var y int64
x = y // 错误：无法将类型为int64的y赋值给time.Duration
链接：https://play.golang.org/p/oD5LwJl7an
英文:
I thought go didn't allow any named type to actual type assignment without explicit type conversion.
But how does it compile without an error if I assign []byte to json.RawMessage?
var a json.RawMessage // type RawMessage []byte
var b []byte
a = b
var x time.Duration // type Duration int64
var y int64
x = y // ERROR: cannot use y (type int64) as type time.Duration in assignment
答案1
得分: 6
int64是一个命名类型，[]byte是一个无名类型。
命名类型通过（可能带限定符的）类型名称来指定；无名类型使用类型字面值来指定，它从现有类型组合成一个新类型 - golang spec
另外
如果两个命名类型的类型名称源自相同的TypeSpec，则它们是相同的。命名类型和无名类型始终不同。如果对应的类型字面值相同，那么两个无名类型是相同的，也就是说，它们具有相同的字面结构，并且相应的组件具有相同的类型 - golang spec
因此
type MyByteArray []byte
type MyInt int
var a MyByteArray
var b []byte
a = b // 合法，因为数组是无名的 - 它们对应的类型字面值是相同的
var x MyInt
var y int
x = y // 非法，因为int是命名类型 - 它们不是源自相同的类型规范
英文:
int64 is a named type, []byte is an unamed type.
> Named types are specified by a (possibly qualified) type name; unnamed types are specified using a type literal, which composes a new type from existing types - golang spec
Also
> Two named types are identical if their type names originate in the same TypeSpec. A named and an unnamed type are always different. Two unnamed types are identical if the corresponding type literals are identical, that is, if they have the same literal structure and corresponding components have identical types. - golang spec
Therefore
type MyByteArray []byte
type MyInt int
var a MyByteArray
var b []byte
a = b // legal because array is unnamed - their corresponding type literals are identical
var x MyInt
var y int
x = y // illegal because int is named - they don't originate in the same type spec
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论