How to Access Fields in a Struct Pointer using `reflect.Value.FieldByName()` in Go?

Calling `reflect.Value.FieldByName() on Pointer Value

In Go, when using reflection with struct pointers, attempting to call reflect.Value.FieldByName() on the struct's pointer value can result in the following error:

reflect: call of reflect.Value.FieldByName on ptr Value

Problem
This error occurs when you try to access a field of a struct value that is being represented as a pointer. Consider the following example:

type Family struct {
  first string
  last string
}
type Person struct {
  name string
  family *Family // Pointer to Family struct
}

func Check(data interface{}) {
  v := reflect.ValueOf(data)
  if v.Kind() == reflect.Struct {
    v = v.FieldByName("family").FieldByName("last")
  }
}

When running this code, the error will occur because the family field is a pointer.

Solution
To resolve this issue, you need to dereference the pointer value using reflect.Indirect() to get the actual struct value before accessing the field:

v = reflect.Indirect(v.FieldByName("family")).FieldByName("last")

With this modification, the code will correctly access the last field of the Family struct, regardless of whether family is a value or a pointer.

Explanation
reflect.Indirect() returns the value that the pointer points to. So, in this case, it returns the Family struct value, which is then accessible via FieldByName().

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