CODEWITHSUNDEEP
gostructreflectioninterface
David Bryant
David Bryant

Reputation: 29

How to modify a field in a struct of an unknown type?

I have multiple structs that have one common field; let's call it common here

type Struct1 struct {
    foo string
    bar string

    common string
}

type Struct2 struct {
    baz int
    qux string

    common string
}

I want to create a function that takes an Interface as input and nullifies common. The available struct types won't be known at compile time, so I can't create a separate function for each type, and I can't use a switch statement.

P.S: In my use-case, I want to nullify common because it holds the creation time of each struct, and I want to track the history of the struct, so I will know if it changes. Having the creation time inside the struct will mess this up because the creation time will be different every time a new struct is generated even though its actual data may be the same.

Upvotes: 0

Views: 570

Answers (1)

svsd
svsd

Reputation: 1869

Define a struct with the common fields and make it implement an interface which says that it is able to nullify the common fields. Then embed this struct into your other struct types that should be able to nullify the fields.

// CommonNullifier is able to nullify its common field(s)
type CommonNullifier interface {
        NullifyCommon()
}

// StructCommon contains the common struct fields
type StructCommon struct {
        Common string
}

func (sc *StructCommon) NullifyCommon() {
        sc.Common = ""
}

// Struct1 embeds common fields, thus implements CommonNullifier
type Struct1 struct {
        StructCommon
        Foo string
}

// Struct2 also embeds common fields, thus also implements CommonNullifier
type Struct2 struct {
        StructCommon
        Bar string
}

// NullifyCommon nullfies the 'common' fields in the argument
func NullifyCommon(s CommonNullifier) {
        s.NullifyCommon()
}

(See it on the Go Playground)

You could also use reflection, but using an interface is generally more readable.

Upvotes: 2

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