drd99007 2018-09-20 21:18
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如何在UnmarshalJSON中调用json.Unmarshal而不引起堆栈溢出?

How can I create a method UnmarshalJSON inside a struct, use json.Unmarshal inside without causing stack overflow?

package xapo

type Xapo struct {}

func (x Xapo) UnmarshalJSON(data []byte) error {
    err := json.Unmarshal(data, &x)
    if err != nil {
        return err
    }
    fmt.Println("done!")
    return nil
}

Can someone explain me why the stack overflow happens? Can it be fixed?

Thanks in advance.

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1条回答 默认 最新

  • doushe2513 2018-09-20 21:35
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    It looks like you may be trying to do custom unmarshaling by using the default unmarshaler and then post-processing the data. However, as you've discovered, the obvious way of trying this causes an infinite loop!

    The usual workaround is to create a new type using your type, use the default unmarshaler on an instance of the new type, post-process the data, and then finally cast to the original type and assign back to the target instance. Note that you'll want to implement UnmarshalJSON on a pointer type.

    For example:

    func (x *Xapo) UnmarshalJSON(data []byte) error {
      // Create a new type from the target type to avoid recursion.
      type Xapo2 Xapo
    
      // Unmarshal into an instance of the new type.
      var x2 Xapo2
      err := json.Unmarshal(data, &x2)
      if err != nil {
        return err
      }
    
      // Perform post-processing here.
      // TODO
    
      // Cast the new type instance to the original type and assign.
      *x = Xapo(x2)
      return nil
    }
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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