Why Use Underscore Empty Struct Fields for Keyed Initialization in Go?

Purpose of Underscore Empty Struct Fields

In Go, it's possible to define structs with a field named "_" containing an empty struct. This idiom enforces keyed field initialization, where every field must be explicitly named when creating an instance of the struct.

Code Example

type SomeType struct {
  Field1 string
  Field2 bool
  _      struct{}
}

Keyed Field Initialization

With this empty struct field, the struct must be declared using keyed fields:

// ALLOWED:
bar := SomeType{Field1: "hello", Field2: true}

// COMPILE ERROR:
foo := SomeType{"hello", true}

Benefits

This technique has several benefits:

• Enforcement of keyed fields: It prevents accidental assignment of fields by position, potentially leading to errors.
• Future-proofing: Empty struct fields allow new fields to be added to the struct in the future without affecting existing code. This maintains backward compatibility and ensures that code that references keyed fields will continue to work correctly.

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