英文:
Numeric and String Operations in Golang
问题
以下是翻译好的内容：
func nextInt(b []byte, i int) (int, int) {
for ; i < len(b) && !isDigit(b[i]); i++ {
}
x := 0
for ; i < len(b) && isDigit(b[i]); i++ {
x = x*10 + int(b[i]) - '0'
}
return x, i
}
我不知道上述代码中以下部分是什么操作。
int(b[i]) - '0'
这是一个数字和字符串相减，但是这是什么样的计算呢？
在官方文档或类似的地方可以找到吗？
英文:
https://go.dev/doc/effective_go
func nextInt(b []byte, i int) (int, int) {
for ; i < len(b) && !isDigit(b[i]); i++ {
}
x := 0
for ; i < len(b) && isDigit(b[i]); i++ {
x = x*10 + int(b[i]) - '0'
}
return x, i
}
I don't know what kind of operation the following part of the above code is.
int(b[i]) - '0'
It's a subtraction of a number and a string, but what kind of calculation is it?
Where can I find it in the official documentation or something similar?
答案1
得分: 1
在Go语言中，单引号括起来的字面量的类型是rune。rune是int32的别名，但更重要的是，它表示字符的Unicode码点值。
你可以在这篇博文"Go中的字符串、字节、符文和字符"中了解一些背景知识。
b []byte（字节切片）被nextInt函数解释为一系列Unicode字符的UTF-8表示。幸运的是，对于ASCII数字，你只需要8位（一个byte）来表示字符，而不是一个完整的rune。
数字0到9的ASCII值是Unicode码点集的一个子集，它们直接相邻。因此，如果你取一个数字的ASCII值，并从ASCII值为零的数字的ASCII值中减去它，你就得到了该数字的数值。
这就是这里发生的事情。
一个小细节是，在Go中，通常你只能从彼此完全相同类型的值中相减。而在这种情况下，你不能从一个rune中减去一个int。但是在Go中，常量是无类型的。它们只有一个默认类型（'0'的默认类型是rune），但会自动强制转换以符合上下文，所以'0'最终具有有效类型int。
英文:
The type of a single-quoted literal in Go is rune.
rune is an alias for int32, but more importantly, it represents the Unicode codepoint value for a character.
You can read some background in this blog post on "Strings, bytes, runes and characters in Go"
The b []byte (slice of bytes) is interpreted by the nextInt function as a the UTF-8 representation of a series of Unicode characters. Luckily, for ASCII numeric digits, you only need 8 bits (a byte) to represent the character, not a full rune.
The ASCII value, which is a subset of the Unicode codepoint set, of the digits 0 to 9 are following each directly. So if you take the ASCII value of a digit, and you subtract the ASCII value of the digit zero from it, you end up with the numeric value of the digit.
That's what is happening here.
A minor detail is that in Go, normally you can only subtract values of exactly the same type from each other. And in this case, you wouldn't be able to subtract a rune from an int. But constants in Go are untyped. They only have a default type ('0' has default type rune) but are automatically coerced to comply with the context, so '0' ends up having the effective type int.
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