@dacapoday
@exonuclease
起初我也想过会不会“ len 的语义更接近于表示数据的尺寸，而非容器的容量或长度”。然而官方文档告诉我们：

func len(v Type) int

The len built-in function returns the length of v, according to its type:

Array: the number of elements in v.
Pointer to array: the number of elements in *v (even if v is nil).
Slice, or map: the number of elements in v; if v is nil, len(v) is zero.
String: the number of bytes in v.
Channel: the number of elements queued (unread) in the channel buffer;
if v is nil, len(v) is zero.

可见除了 string 之外，其余类型作为 len 函数的参数获取到的都是“容器的容量或长度”