关于golang:70-Go-中不常注意的各种细节集锦-Go-夜读

原视频: https://www.bilibili.com/vide...

1. 打印true还是false?

func f() bool {    return false}func main() {    switch f()     {    case true:        fmt.Println("true")    case false:        fmt.Println("false")    }}

等价于

func f() bool {    return false}func main() {    switch f();    false {    case true:        fmt.Println("true")    case false:        fmt.Println("false")    }}

2. os.Exit(包含log.Fatal等)的时候不会调用defer

3. runtime.Goexit调用后会调用defer

4. 估值后果因是否为变量或者常量而异

例1：

func main() {    var n uint = 10    const N uint = 10    var x byte = (1 << n) / 100        // 1被推断出byte，溢出    var y byte = (1 << N) / 100        // 1被推断不确定数    fmt.Println(x)        // 0    fmt.Println(y)        // 100}

例2：

func main() {    var n uint = 10    const N uint = 10    var x float64 = (1 << n) / 100        // 1被推断出float64，报错    var y float64 = (1 << N) / 100        // 1被推断不确定数    fmt.Println(x)    fmt.Println(y)}

例2编译报错

多值赋值

package mainfunc assign1() {    a, b := 1, 2    a, b = b, a}func assign2() {    var a []int    a, a[0] = []int{2112321}, 212121}func main() {     assign1()     assign2()}

执行后go tool compile -N -l -S ./assignment.go > ./assignment.s

"".assign1 STEXT nosplit size=69 args=0x0 locals=0x20 funcid=0x0    0x0000 00000 (./assignment.go:3)    TEXT    "".assign1(SB), NOSPLIT|ABIInternal, $32-0    0x0000 00000 (./assignment.go:3)    SUBQ    $32, SP    0x0004 00004 (./assignment.go:3)    MOVQ    BP, 24(SP)    0x0009 00009 (./assignment.go:3)    LEAQ    24(SP), BP    0x000e 00014 (./assignment.go:4)    MOVQ    $1, "".a+8(SP)                       // a = 1    0x0017 00023 (./assignment.go:4)    MOVQ    $2, "".b(SP)                         // b = 2    0x001f 00031 (./assignment.go:5)    MOVQ    "".a+8(SP), AX                       // AX = a = 1    0x0024 00036 (./assignment.go:5)    MOVQ    AX, ""..autotmp_2+16(SP)             // autotmp_2 = AX = a = 1    0x0029 00041 (./assignment.go:5)    MOVQ    "".b(SP), AX                         // AX = b = 2    0x002d 00045 (./assignment.go:5)    MOVQ    AX, "".a+8(SP)                       // a = AX = 2    0x0032 00050 (./assignment.go:5)    MOVQ    ""..autotmp_2+16(SP), AX             // AX = autotmp_2 = a = 1    0x0037 00055 (./assignment.go:5)    MOVQ    AX, "".b(SP)                         // b = AX    0x003b 00059 (./assignment.go:6)    MOVQ    24(SP), BP    0x0040 00064 (./assignment.go:6)    ADDQ    $32, SP    0x0044 00068 (./assignment.go:6)    RET                    H.. ."".assign2 STEXT nosplit size=192 args=0x0 locals=0x70 funcid=0x0    0x0000 00000 (./assignment.go:8)    TEXT    "".assign2(SB), NOSPLIT|ABIInternal, $112-0    0x0000 00000 (./assignment.go:8)    SUBQ    $112, SP    0x0004 00004 (./assignment.go:8)    MOVQ    BP, 104(SP)    0x0009 00009 (./assignment.go:8)    LEAQ    104(SP), BP    0x000e 00014 (./assignment.go:9)    MOVQ    $0, "".a+32(SP)    0x0017 00023 (./assignment.go:9)    XORPS    X0, X0    0x001a 00026 (./assignment.go:9)    MOVUPS    X0, "".a+40(SP)                        // a a []int = nil    0x001f 00031 (./assignment.go:10)    MOVQ    $0, ""..autotmp_4+16(SP)                   0x0028 00040 (./assignment.go:10)    LEAQ    ""..autotmp_4+16(SP), DX                   0x002d 00045 (./assignment.go:10)    MOVQ    DX, ""..autotmp_2+24(SP)          0x0032 00050 (./assignment.go:10)    TESTB    AL, (DX)    0x0034 00052 (./assignment.go:10)    MOVQ    $2112321, ""..autotmp_4+16(SP)       0x003d 00061 (./assignment.go:10)    TESTB    AL, (DX)    0x003f 00063 (./assignment.go:10)    NOP    0x0040 00064 (./assignment.go:10)    JMP    66    0x0042 00066 (./assignment.go:10)    MOVQ    DX, ""..autotmp_1+80(SP)                   0x0047 00071 (./assignment.go:10)    MOVQ    $1, ""..autotmp_1+88(SP)                   0x0050 00080 (./assignment.go:10)    MOVQ    $1, ""..autotmp_1+96(SP)                // 00031-00080: autotmp_1 = []int{2112321}        0x0059 00089 (./assignment.go:10)    MOVQ    "".a+32(SP), DX                             0x005e 00094 (./assignment.go:10)    MOVQ    "".a+40(SP), BX    0x0063 00099 (./assignment.go:10)    MOVQ    "".a+48(SP), SI    0x0068 00104 (./assignment.go:10)    MOVQ    DX, ""..autotmp_5+56(SP)    0x006d 00109 (./assignment.go:10)    MOVQ    BX, ""..autotmp_5+64(SP)    0x0072 00114 (./assignment.go:10)    MOVQ    SI, ""..autotmp_5+72(SP)                // 00089-00114: autotmp_5 = copy(a)    0x0077 00119 (./assignment.go:10)    MOVQ    ""..autotmp_1+80(SP), DX    0x007c 00124 (./assignment.go:10)    MOVQ    ""..autotmp_1+88(SP), BX    0x0081 00129 (./assignment.go:10)    MOVQ    ""..autotmp_1+96(SP), SI    0x0086 00134 (./assignment.go:10)    MOVQ    DX, "".a+32(SP)    0x008b 00139 (./assignment.go:10)    MOVQ    BX, "".a+40(SP)    0x0090 00144 (./assignment.go:10)    MOVQ    SI, "".a+48(SP)                          // 00119-00144: a = autotmp_1    0x0095 00149 (./assignment.go:10)    MOVQ    ""..autotmp_5+64(SP), CX    0x009a 00154 (./assignment.go:10)    MOVQ    ""..autotmp_5+56(SP), DX    0x009f 00159 (./assignment.go:10)    NOP    0x00a0 00160 (./assignment.go:10)    TESTQ    CX, CX                                    // if CX != 0    0x00a3 00163 (./assignment.go:10)    JHI    167                                       // CX != 0,跳167    0x00a5 00165 (./assignment.go:10)    JMP    184                                       // CX == 0, 跳184    0x00a7 00167 (./assignment.go:10)    MOVQ    $212121, (DX)    0x00ae 00174 (./assignment.go:11)    MOVQ    104(SP), BP    0x00b3 00179 (./assignment.go:11)    ADDQ    $112, SP    0x00b7 00183 (./assignment.go:11)    RET    0x00b8 00184 (./assignment.go:10)    XORL    AX, AX    0x00ba 00186 (./assignment.go:10)    PCDATA    $1, $0    0x00ba 00186 (./assignment.go:10)    CALL    runtime.panicIndex(SB)    0x00bf 00191 (./assignment.go:10)    XCHGL    AX, AX

所以最初assign2会抛异样
又例如:

func assign3() {    var c = []int{1, 2, 3}    d := c    c, c[0] = []int{2112321}, 101    fmt.Println(c)                   // [2112321]    fmt.Println(d)                   // [101 2 3]}