go - 尝试使用指针字段初始化结构时出现nil指针取消引用错误

Question

定义的结构类型:

type ValidateTemplateQuery struct {
    TemplateURL  *string `json:"template_url" valid:"optional"`
    TemplateBody *string `json:"template_body" valid:"optional"`
}

尝试使用模拟值初始化:

action := &ValidateTemplateQuery{
    TemplateURL:  *("TemplateURLValue"),
    TemplateBody: *("TemplateBodyValue"),
}

错误

getting "panic: runtime error: invalid memory address or nil pointer dereference"

Answer 1

trying to initiate with mock values

使用变量的地址。例如，

package main

import (
    "fmt"
)

func main() {

    type ValidateTemplateQuery struct {
        TemplateURL  *string `json:"template_url" valid:"optional"`
        TemplateBody *string `json:"template_body" valid:"optional"`
    }

    url := "TemplateURLValue"
    body := "TemplateBodyValue"
    action := &ValidateTemplateQuery{
        TemplateURL:  &url,
        TemplateBody: &body,
    }

    fmt.Println(action, *action.TemplateURL, *action.TemplateBody)
}

游乐场:https://play.golang.org/p/LZKV2LZ4KiE

输出:

&{0x40c138 0x40c140} TemplateURLValue TemplateBodyValue

The Go Programming Language Specification

Address operators

For an operand x of type T, the address operation &x generates a pointer of type *T to x. The operand must be addressable, that is, either a variable, pointer indirection, or slice indexing operation; or a field selector of an addressable struct operand; or an array indexing operation of an addressable array. As an exception to the addressability requirement, x may also be a (possibly parenthesized) composite literal. If the evaluation of x would cause a run-time panic, then the evaluation of &x does too.