This technique enforces keyed fields when declaring a struct.
For example, the struct:
type SomeType struct { Field1 string Field2 bool _ struct{} } can only be declared with keyed fields:
// ALLOWED: bar := SomeType{Field1: "hello", Field2: "true"true} // COMPILE ERROR: foo := SomeType{"hello", true} One reason for doing this is to allow additional fields to be added to the struct in the future without breaking existing code.