Can Go Interfaces Effectively Represent Data?

Go Interface Fields: A Study in Data Access

Go interfaces are known for defining functionality rather than data. While one can specify methods in an interface, fields cannot be declared directly.

type Giver interface {
    Give() int64
}

This behavior raises the question of whether it is possible to define an interface that represents data. While not directly possible, there is a workaround that involves embedded structs and the GetPerson() method.

type PersonProvider interface {
    GetPerson() *Person
}

type Person struct {
    Name string
    Age  int64
}

type Bob struct {
    FavoriteNumber int64
    Person
}

By defining an interface that specifies a GetPerson() method, one can effectively expose data to functions that are designed to use that interface.

func DoBirthday(pp PersonProvider) {
    pers := pp.GetPerson()
    pers.Age += 1
}

However, it is crucial to note that this method does not eliminate direct access to data. It only provides an abstraction layer that can be utilized for specific purposes.

Pros and Cons: A Balanced Perspective

While this workaround can be a useful technique, it is essential to weigh its pros and cons carefully.

Pros:

• Adds flexibility for future changes by hiding data behind a method call.
• Facilitates the addition of logic or validation when interacting with the data.
• Helps avoid cyclic imports in scenarios where the interface is implemented without importing the package defining it.

Cons:

• Pointers are still exposed, potentially allowing direct access to the underlying data.
• Go conventions generally discourage excessive abstraction over data attributes.
• May lead to unnecessary complexity if getters and setters are used excessively.

Ultimately, the decision of whether or not to use this technique depends on the specific use case and the potential for future changes. If it is highly likely that exposure of the data could complicate future implementation, using getter/setter methods becomes more compelling.

However, if the interface is only used within a single project and the data remains relatively stable, it may be simpler and more efficient to expose the data directly without an abstraction layer.

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