英文:
"wrap it in a bufio.NewReader if it doesn't support ReadByte" pattern
问题
以下是一个Go库的片段。请问有人可以指出r.(byteReader)的重要性吗？对于一个初学者来说，语法的使用并不明显。byteReader是一个定义的接口，似乎不是io.Reader的成员。由于这似乎是一种巧妙的代码，有人可以提供一些见解吗？
作者提到了"如果不支持ReadByte，则将其包装在bufio.NewReader中"的模式。https://github.com/dave-andersen/deltagolomb/blob/master/deltagolomb.go
type byteReader interface {
io.Reader
ReadByte() (c byte, err error)
}
func makeReader(r io.Reader) byteReader {
if rr, ok := r.(byteReader); ok {
return rr
}
return bufio.NewReader(r)
}
英文:
Following is a snippet from one of the Go libs. Could anyone please point out the significance of r.(byteReader)? The syntax usage is not very obvious to a novice. byteReader is a defined interface and does not seem to be the member of io.Reader. Since, this seems to be some kind of nifty code, can anyone provide some insight.
The author mentions: "wrap it in a bufio.NewReader if it doesn't support ReadByte" pattern. https://github.com/dave-andersen/deltagolomb/blob/master/deltagolomb.go
type byteReader interface {
io.Reader
ReadByte() (c byte, err error)
}
func makeReader(r io.Reader) byteReader {
if rr, ok := r.(byteReader); ok {
return rr
}
return bufio.NewReader(r)
}
答案1
得分: 6
r.(byteReader)被称为类型断言。即使io.Reader本身没有实现byteReader接口，但存储在r中的值仍然有可能实现了byteReader接口。因此，通过进行类型断言，你可以确定是否满足这种情况：
规范中指出：
> x.(T)断言x不是nil，并且存储在x中的值是类型T。表示为x.(T)的符号被称为类型断言。
> ...
> 如果T是一个接口类型，x.(T)断言x的动态类型实现了接口T。
编辑
注释中的“将其包装在bufio.NewReader中”是指makeReader提供的io.Reader；如果它没有实现byteReader，makeReader将其包装在实现了byteReader的bufio.Reader中，并返回它。
英文:
r.(byteReader) is called a type assertion. Even if io.Reader doesn't implement the byteReader interface in itself, it it still possible that the value stored in r might implement byteReader. So, by doing the type assertion, you can assert if that is the case:
The specification states:
> x.(T) asserts that x is not nil and that the value stored in x is of
> type T. The notation x.(T) is called a type assertion.
> ...
> If T is
> an interface type, x.(T) asserts that the dynamic type of x implements
> the interface T.
Edit
The comment, "wrap it in a bufio.NewReader", refers to makeReader's provided io.Reader; if it doesn't implement byteReader, makeReader will wrap it in a bufio.Reader which does implement bytesReader, and return it instead.
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