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关于go:go切片复制-copy-更像是一种指定开始索引的替换

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一、语法

go 语言的内置函数 copy() 能够将一个数组切片复制到另一个数组切片中，如果退出的两个数组切片不一样大，就会依照其中较小的那个数组切片的元素个数进行复制。

func copy(dst, src []Type) int
应用 copy 有几个特色

  1. 如果之前是两个不同的地址，copy 后也是两个不同的地址，扭转其中一个不影响另一个。
  2. copy 到指标 slice，到底复制多少，取决于它的大小以及起始地位。
  3. 更像是一种指定开始索引的替换

二、应用示范

1、同样的大小 

func TestCopy1(t *testing.T) {from := []int{1, 2, 3}
    var to []int = make([]int, len(from), cap(from))
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    copy(to, from)
    t.Log("copy(to, from) 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    to[0] = 11
    t.Log("to[0] = 11 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)
}

输入：

from slice: [1 2 3], address: 0xc0000cc060
to slice: [0 0 0], address: 0xc0000cc080
copy(to[2:], from) 后：from slice: [1 2 3], address: 0xc0000cc060
to slice: [1 2 3], address: 0xc0000cc080
to[0] = 11 后：from slice: [1 2 3], address: 0xc0000cc060
to slice: [11 2 3], address: 0xc0000cc080

2、指标的 slice 为长度 len 为 0 的时候，复制不胜利，还是为空 []

func TestCopy2(t *testing.T) {from := []int{1, 2, 3}
    var to []int = make([]int, 0, cap(from))
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    copy(to, from)
    t.Log("copy(to, from) 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)
}

输入：

from slice: [1 2 3], address: 0xc000144060
to slice: [], address: 0xc000144080
copy(to, from) 后：from slice: [1 2 3], address: 0xc000144060
to slice: [], address: 0xc000144080

3、指标的 slice 为长度 len 为 1 的时候，只能复制第一个 

func TestCopy3(t *testing.T) {from := []int{1, 2, 3}
    var to []int = make([]int, 1, cap(from))
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    copy(to, from)
    t.Log("copy(to, from) 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)
}

输入：

from slice: [1 2 3], address: 0xc0000cc060
to slice: [0], address: 0xc0000cc080
copy(to, from) 后：from slice: [1 2 3], address: 0xc0000cc060
to slice: [1], address: 0xc0000cc080

4、指标的 slice 为长度 len 远大于的时候，替换开始的一部分 

func TestCopy4(t *testing.T) {from := []int{1, 2, 3}
    var to []int = make([]int, 10, 10)
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    copy(to, from)
    t.Log("copy(to, from) 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)
}

输入：

from slice: [1 2 3], address: 0xc000016160
to slice: [0 0 0 0 0 0 0 0 0 0], address: 0xc0000200f0
copy(to, from) 后：from slice: [1 2 3], address: 0xc000016160
to slice: [1 2 3 0 0 0 0 0 0 0], address: 0xc0000200f0

5、指定开始的替换索引 copy(to[3:], from)

func TestCopy5(t *testing.T) {from := []int{1, 2, 3}
    var to []int = make([]int, 10, 10)
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)
    t.Logf("to slice: %[1]v, address: %[1]p\n", to)

    copy(to[3:], from)
    t.Log("copy(to[3:], from) 后：")
    t.Logf("from slice: %[1]v, address: %[1]p\n", from)

输入：

from slice: [1 2 3], address: 0xc000016160
to slice: [0 0 0 0 0 0 0 0 0 0], address: 0xc0000200f0
copy(to[3:], from) 后：from slice: [1 2 3], address: 0xc000016160
to slice: [0 0 0 1 2 3 0 0 0 0], address: 0xc0000200f0
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