type slice struct {
    array unsafe.Pointer
    len   int
    cap   int
}

func main() {
    var nums []int  // 聲明切片
    fmt.Println(len(nums), cap(nums)) // 0 0
    nums = append(nums, 1)   // 初始化
    fmt.Println(len(nums), cap(nums)) // 1 1

    nums1 := []int{1,2,3,4}    // 聲明并初始化
    fmt.Println(len(nums1), cap(nums1))    // 4 4

    nums2 := make([]int,3,5)   // 使用make()函數(shù)構(gòu)造切片
    fmt.Println(len(nums2), cap(nums2))    // 3 5
}

func Append(slice []int, items ...int) []int

package main

import "fmt"

func main() {
    s := []int{1, 2, 3}
    fmt.Println("初始切片:", s)

    s = append(s, 4, 5, 6)
    fmt.Println("追加多個(gè)值后的切片:", s)
}

初始切片: [1 2 3]
追加多個(gè)值后的切片: [1 2 3 4 5 6]

package main

import "fmt"

func main() {
    s1 := []int{1, 2, 3}
    fmt.Println("初始切片:", s1)

    s2 := []int{4, 5, 6}
    s1 = append(s1, s2...)
    fmt.Println("追加另一個(gè)切片后的切片:", s1)
}

初始切片: [1 2 3]
追加另一個(gè)切片后的切片: [1 2 3 4 5 6]

package main

import "fmt"

func main() {
    s := make([]int, 0, 3) // 創(chuàng)建一個(gè)長(zhǎng)度為0，容量為3的切片
    fmt.Printf("初始狀態(tài): len=%d cap=%d %v\n", len(s), cap(s), s)

    for i := 1; i <= 5; i++ {
        s = append(s, i) // 向切片中添加元素
        fmt.Printf("添加元素%d: len=%d cap=%d %v\n", i, len(s), cap(s), s)
    }
}

初始狀態(tài): len=0 cap=3 []
添加元素1: len=1 cap=3 [1]
添加元素2: len=2 cap=3 [1 2]
添加元素3: len=3 cap=3 [1 2 3]
添加元素4: len=4 cap=6 [1 2 3 4]
添加元素5: len=5 cap=6 [1 2 3 4 5]

slice = append(slice, elem)

package main

import "fmt"

func main() {
    s := make([]int, 0)

    oldCap := cap(s)

    for i := 0; i < 2048; i++ {
        s = append(s, i)

        newCap := cap(s)

        if newCap != oldCap {
            fmt.Printf("[%d -> %4d] cap = %-4d  |  after append %-4d  cap = %-4d\n", 0, i-1, oldCap, i, newCap)
            oldCap = newCap
        }
    }
}

[0 ->   -1] cap = 0     |  after append 0     cap = 1   
[0 ->    0] cap = 1     |  after append 1     cap = 2   
[0 ->    1] cap = 2     |  after append 2     cap = 4   
[0 ->    3] cap = 4     |  after append 4     cap = 8   
[0 ->    7] cap = 8     |  after append 8     cap = 16  
[0 ->   15] cap = 16    |  after append 16    cap = 32  
[0 ->   31] cap = 32    |  after append 32    cap = 64  
[0 ->   63] cap = 64    |  after append 64    cap = 128 
[0 ->  127] cap = 128   |  after append 128   cap = 256 
[0 ->  255] cap = 256   |  after append 256   cap = 512 
[0 ->  511] cap = 512   |  after append 512   cap = 1024
[0 -> 1023] cap = 1024  |  after append 1024  cap = 1280
[0 -> 1279] cap = 1280  |  after append 1280  cap = 1696
[0 -> 1695] cap = 1696  |  after append 1696  cap = 2304

[0 ->   -1] cap = 0     |  after append 0     cap = 1
[0 ->    0] cap = 1     |  after append 1     cap = 2   
[0 ->    1] cap = 2     |  after append 2     cap = 4   
[0 ->    3] cap = 4     |  after append 4     cap = 8   
[0 ->    7] cap = 8     |  after append 8     cap = 16  
[0 ->   15] cap = 16    |  after append 16    cap = 32  
[0 ->   31] cap = 32    |  after append 32    cap = 64  
[0 ->   63] cap = 64    |  after append 64    cap = 128 
[0 ->  127] cap = 128   |  after append 128   cap = 256 
[0 ->  255] cap = 256   |  after append 256   cap = 512 
[0 ->  511] cap = 512   |  after append 512   cap = 848 
[0 ->  847] cap = 848   |  after append 848   cap = 1280
[0 -> 1279] cap = 1280  |  after append 1280  cap = 1792
[0 -> 1791] cap = 1792  |  after append 1792  cap = 2560

// src/runtime/slice.go

func growslice(et *_type, old slice, cap int) slice {
    // ...

    newcap := old.cap
    doublecap := newcap + newcap
    if cap > doublecap {
        newcap = cap
    } else {
        if old.cap < 1024 {
            newcap = doublecap
        } else {
            // Check 0 < newcap to detect overflow
            // and prevent an infinite loop.
            for 0 < newcap && newcap < cap {
                newcap += newcap / 4
            }
            // Set newcap to the requested cap when
            // the newcap calculation overflowed.
            if newcap <= 0 {
                newcap = cap
            }
        }
    }

    // ...

    return slice{p, old.len, newcap}
}

// src/runtime/slice.go

func growslice(et *_type, old slice, cap int) slice {
    // ...

    newcap := old.cap
    doublecap := newcap + newcap
    if cap > doublecap {
        newcap = cap
    } else {
        const threshold = 256
        if old.cap < threshold {
            newcap = doublecap
        } else {
            // Check 0 < newcap to detect overflow
            // and prevent an infinite loop.
            for 0 < newcap && newcap < cap {
                // Transition from growing 2x for small slices
                // to growing 1.25x for large slices. This formula
                // gives a smooth-ish transition between the two.
                newcap += (newcap + 3*threshold) / 4
            }
            // Set newcap to the requested cap when
            // the newcap calculation overflowed.
            if newcap <= 0 {
                newcap = cap
            }
        }
    }

    // ...

    return slice{p, old.len, newcap}
}