golang查看channel緩衝區的長度

golang提供內建函數cap用於查看channel緩衝區長度。golang

cap的定義以下：函數

func cap(v Type) int 
The cap built-in function returns the capacity of v, according to its type: 
- Array: the number of elements in v (same as len(v)).等同於len

- Pointer to array: the number of elements in *v (same as len(v)).等同於len

- Slice: the maximum length the slice can reach when resliced;
if v is nil, cap(v) is zero.對於slice，表示在不從新分配空間的狀況下，能夠達到的切片的最大長度。若是切片是nil， 則長度爲0.

-  Channel: the channel buffer capacity, in units of elements;表示緩衝區的長度。
if v is nil, cap(v) is zero. 若是通道是nil，則緩衝區長度爲0。

Example

package main

import ("fmt")

func main(){

    ch1 := make(chan int)
    ch2 := make(chan int, 2)//緩衝區長度爲2

    fmt.Println("ch1 buffer len:", cap(ch1))
    fmt.Println("ch2 buffer len:", cap(ch2))
}

output:ui

ch1 buffer len:0
ch2 buffer len:2code