go - 使用反射模板创建值时的意外故障地址

Question

我想通过反射最小化类型testData，但是得到了意外的错误地址

func TestData(t *testing.T) {
    tpl, err := template.New("ok").Parse("{{.Ok}}")
    if err != nil {
        panic(err)
    }
    buf := bytes.NewBuffer(nil)
    myTyp := reflect.StructOf([]reflect.StructField{
        {Name: "MyFace", Type: reflect.TypeOf((*MyFace)(nil)).Elem(), Index: []int{0}, Anonymous: true},
    })
    myVal := reflect.New(myTyp).Elem()
    myVal.Field(0).Set(reflect.ValueOf(MyFace(&testFace{})))
    err = tpl.Execute(buf, myVal.Interface()) // unexpected fault address
    //err = tpl.Execute(buf, &testDat{MyFace: MyFace(&testFace{})}) // works as expected
    if err != nil {
        panic(err)
    }
    fmt.Println(buf.String())
}

type testData struct {
    MyFace
}
type testFace struct {
}

func (testFace) Ok() string {
    return "All right"
}

type MyFace interface {
    Ok() string
}

错误

unexpected fault address 0xc4200e83a0
[signal SIGBUS: bus error code=0x2 addr=0xc4200e83a0 pc=0xc4200e83a0]

goroutine 5 [running]:
runtime.throw(0x13728ac, 0x5)
    /usr/local/Cellar/go/1.9.1/libexec/src/runtime/panic.go:605 +0x95 fp=0xc420058fe8 sp=0xc420058fc8 pc=0x102d235
runtime.sigpanic()
    /usr/local/Cellar/go/1.9.1/libexec/src/runtime/signal_unix.go:364 +0x29d fp=0xc420059038 sp=0xc420058fe8 pc=0x1043c2d
runtime.call32(0xc42007f260, 0xc42000e0a8, 0xc4200e8560, 0x800000018)
    /usr/local/Cellar/go/1.9.1/libexec/src/runtime/asm_amd64.s:509 +0x3b fp=0xc420059068 sp=0xc420059038 pc=0x105a51b
reflect.Value.call(0xc42009ca00, 0xc420048e10, 0x293, 0x1372569, 0x4, 0x155f1b8, 0x0, 0x0, 0x13711a0, 0x1, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/reflect/value.go:434 +0x906 fp=0xc420059340 sp=0xc420059068 pc=0x10b1c76
reflect.Value.Call(0xc42009ca00, 0xc420048e10, 0x293, 0x155f1b8, 0x0, 0x0, 0x150f5c0, 0xc420064300, 0xc420064300)
    /usr/local/Cellar/go/1.9.1/libexec/src/reflect/value.go:302 +0xa4 fp=0xc4200593a8 sp=0xc420059340 pc=0x10b1254
text/template.(*state).evalCall(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0xc42009ca00, 0xc420048e10, 0x293, 0x150b800, 0xc42007eff0, 0x137307e, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:670 +0x580 fp=0xc4200595e0 sp=0xc4200593a8 pc=0x12b3480
text/template.(*state).evalField(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0x137307e, 0x2, 0x150b800, 0xc42007eff0, 0xc420048d00, 0x1, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:560 +0xd38 fp=0xc420059940 sp=0xc4200595e0 pc=0x12b2d98
text/template.(*state).evalFieldChain(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0xc42009ca00, 0xc420048e10, 0x99, 0x150b800, 0xc42007eff0, 0xc420048cf0, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:528 +0x22a fp=0xc4200599f8 sp=0xc420059940 pc=0x12b1d2a
text/template.(*state).evalFieldNode(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0xc42007eff0, 0xc420048d00, 0x1, 0x1, 0x0, 0x0, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:492 +0x118 fp=0xc420059ab0 sp=0xc4200599f8 pc=0x12b1478
text/template.(*state).evalCommand(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0xc42007efc0, 0x0, 0x0, 0x0, 0x348a0, 0x12fa0e0, ...)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:430 +0x676 fp=0xc420059b60 sp=0xc420059ab0 pc=0x12b0e26
text/template.(*state).evalPipeline(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0xc420088280, 0xc42007f1d0, 0x30, 0x28)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:408 +0x115 fp=0xc420059c58 sp=0xc420059b60 pc=0x12b0315
text/template.(*state).walk(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0x150b620, 0xc42007f020)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:234 +0x4af fp=0xc420059cd8 sp=0xc420059c58 pc=0x12af01f
text/template.(*state).walk(0xc420059dd0, 0xc42009ca00, 0xc420048e10, 0x99, 0x150b920, 0xc42007ef90)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:242 +0x11d fp=0xc420059d58 sp=0xc420059cd8 pc=0x12aec8d
text/template.(*Template).execute(0xc4200107c0, 0x1505a00, 0xc4200fe620, 0xc42009ca00, 0xc420048e10, 0x0, 0x0)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:197 +0x1f9 fp=0xc420059e28 sp=0xc420059d58 pc=0x12ae6c9
text/template.(*Template).Execute(0xc4200107c0, 0x1505a00, 0xc4200fe620, 0xc42009ca00, 0xc420048e10, 0x16, 0x194)
    /usr/local/Cellar/go/1.9.1/libexec/src/text/template/exec.go:180 +0x53 fp=0xc420059e70 sp=0xc420059e28 pc=0x12ae4a3
wenerme/tests/wcwork.TestData(0xc4201020f0)
    /Users/wener/go/src/wenerme/tests/wcwork/types_test.go:241 +0x31f fp=0xc420059fa8 sp=0xc420059e70 pc=0x12c459f
testing.tRunner(0xc4201020f0, 0x1387c28)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:746 +0xd0 fp=0xc420059fd0 sp=0xc420059fa8 pc=0x10efc60
runtime.goexit()
    /usr/local/Cellar/go/1.9.1/libexec/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc420059fd8 sp=0xc420059fd0 pc=0x105cd41
created by testing.(*T).Run
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:789 +0x2de

goroutine 1 [chan receive]:
testing.(*T).Run(0xc420102000, 0x13732b1, 0x8, 0x1387c28, 0x107ab01)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:790 +0x2fc
testing.runTests.func1(0xc420102000)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:1004 +0x64
testing.tRunner(0xc420102000, 0xc420057de0)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:746 +0xd0
testing.runTests(0xc4200e8320, 0x153b700, 0x5, 0x5, 0xc42009c820)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:1002 +0x2d8
testing.(*M).Run(0xc420057f18, 0xc420057f70)
    /usr/local/Cellar/go/1.9.1/libexec/src/testing/testing.go:921 +0x111
main.main()

reflect 有什么问题？

Answer 1

您可以将reflect.Value 直接传递给text/template 和html/template execute 方法。如果您更改代码并直接传递它们并使用 {.MyFace.Ok} 一切正常。我附上我的代码:

package hello

import (
    "bytes"
    "fmt"
    "html/template"
    "reflect"
    "testing"
)

func TestData(t *testing.T) {
    tpl, err := template.New("ok").Parse("{{.MyFace.Ok}}")
    if err != nil {
        panic(err)
    }
    buf := bytes.NewBuffer(nil)
    myTyp := reflect.StructOf([]reflect.StructField{
        {Name: "MyFace", Type: reflect.TypeOf((*MyFace)(nil)).Elem(), Index: []int{0}, Anonymous: true},
    })
    fmt.Println(myTyp)
    myVal := reflect.New(myTyp)
    myVal.Elem().Field(0).Set(reflect.New(reflect.TypeOf(testFace{})).Elem())
    err = tpl.Execute(buf, myVal.Elem()) // unexpected fault address
    //err = tpl.Execute(buf, &testDat{MyFace: MyFace(&testFace{})}) // works as expected
    if err != nil {
        panic(err)
    }
    fmt.Println(buf.String())
}

type testData struct {
    MyFace
}
type testFace struct {
    i int
}

func (testFace) Ok() string {
    return "All right"
}

type MyFace interface {
    Ok() string
}

但是您可以在上面的代码中使用 myVal.Elem().Interface() 来测试所有问题，因为 go 无法在您传递的接口(interface)上找到 Ok 方法。

正如您在 reflect.StructOf 文档中所见，StructOf 当前不会为嵌入字段生成包装器方法。在未来的版本中可能会取消此限制。