英文:
The "cap" of Golang
问题
以下是要翻译的内容：
以下是Go代码：
var numbers4 = [...]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
slice := numbers4[4:6:8]
fmt.Printf("%d\n", cap(slice))
为什么cap(slice)等于4？
我曾经以为应该是2。
英文:
The following go code:
var numbers4 = [...]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
slice := numbers4[4:6:8]
fmt.Printf("%d\n", cap(slice))
Why is cap(slice) equal to 4?
I used to thought that should be 2.
答案1
得分: 4
numbers4[4:6:8] 是一个完整的切片表达式：
> 对于数组、数组指针或切片 a（但不包括字符串），主表达式
>
> a[low : high : max]
>
> 构造了一个与简单切片表达式 a[low : high] 具有相同类型、长度和元素的切片。此外，它通过将结果切片的容量设置为 max - low 来控制结果切片的容量。
规范中指出，完整的切片表达式控制容量，将其限制为 max - low，在你的例子中为 8 - 4 = 4。
容量不是切片可以扩展的“额外”元素，容量是切片可以扩展到的最大长度，包括当前长度 + 超出长度的额外元素。
slice := numbers4[4:6:8]
len(slice) = 6 - 4 = 2
cap(slice) = 8 - 4 = 4
英文:
numbers4[4:6:8] is a full slice expression:
> For an array, pointer to array, or slice a (but not a string), the primary expression
>
> a[low : high : max]
>
> constructs a slice of the same type, and with the same length and elements as the simple slice expression a[low : high]. Additionally, it controls the resulting slice's capacity by setting it to max - low.
The spec says the full slice expression controls the capacity, limiting it to max - low, which in your case is 8 - 4 = 4.
The capacity is not the "extra" elements of which the slice may be extended, the capacity is the max length to which a slice may be extended, which includes current length + extra elements beyond the length.
slice := numbers4[4:6:8]
len(slice) = 6 - 4 = 2
cap(slice) = 8 - 4 = 4
答案2
得分: 3
容量是底层数组中的元素数量（从切片指针所指向的元素开始计算）。
来自Go切片：用法和内部原理。
基本上，它意味着容量(cap)不等于长度(len)。
因此，该切片从#4开始，结束于#8，因此容量(cap)为8 - 4 = 4。
英文:
> The capacity is the number of elements in the underlying array
> (beginning at the element referred to by the slice pointer).
from Go Slices: usage and internals.
Basically, it means cap != len.
So, the slice starts at #4, and finishes at #8, hence, cap is 8 - 4 = 4.
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