How to set default values for multiple fields in a nested struct

Suppose you have the following:

type Animal struct {
	Name string
	Ears int
	Eyes int
}

type Dog struct {
	Animal `default:"Animal{Ears:'2', Eyes:'2'}"`
}

Is there a way to set the default? It doesn't work in the above.

1. default:{Ears:'2', Eyes:'2'}
2. default.Ears:"2", default.Eyes:"2"}

The syntax you're trying to use is not supported. You have to use a constructor function. See https://www.geeksforgeeks.org/how-to-assign-default-value-for-struct-field-in-golang/ for one decent discussion of that approach.

In the code provided, the struct Dog embeds the Animal struct, and there seems to be an attempt to set default values for the Ears and Eyes fields of the embedded Animal struct. However, the syntax used is not valid for setting default values.

In Go, you cannot directly set default values for struct fields using tags like default:"...". Tags are used for other purposes like serialization, but they don't provide a mechanism for setting default values.

If you want to set default values for the fields of the embedded Animal struct in the Dog struct, you have a couple of options:

1) Constructor function:

You can create a constructor function for the Dog struct that initializes the embedded Animal struct with the default values you desire.

    type Animal struct {
            Name string
            Ears int
            Eyes int
        }
        
        type Dog struct {
            Animal
        }
        
        // NewDog creates a new Dog instance with default values for Animal fields.
        func NewDog(name string) *Dog {
            return &Dog{
                Animal: Animal{
                    Name: name,
                    Ears: 2,
                    Eyes: 2,
                },
            }
        }

2) Initialize on declaration:

You can simply set default values when declaring a new instance of the Dog struct.

        type Animal struct {
            Name string
            Ears int
            Eyes int
        }
        
        type Dog struct {
            Animal
        }
        
        func main() {
            myDog := Dog{
                Animal: Animal{
                    Ears: 2,
                    Eyes: 2,
                },
            }
            // You can set the name afterward if needed
            myDog.Name = "Buddy"
        }