Generic Structs

Generic structs can model pairs, containers and records while keeping their field types explicit.

A struct may have several independent type parameters: type Pair[A, B any] struct { First A; Second B }. The two fields need not share the same type. When constructing a generic literal, specify type arguments in its type name.

Generic structs make sense when code works with the container shape regardless of the chosen types. Consider a normal concrete struct when it describes a domain record with fixed fields.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

type Pair[A, B any] struct {
	First  A
	Second B
}

func main() {
	student := Pair[string, int]{First: "Noah", Second: 91}
	coordinate := Pair[float64, float64]{First: 2.5, Second: 4.0}
	fmt.Println("Student:", student.First, student.Second)
	fmt.Println("Coordinate:", coordinate.First, coordinate.Second)
}

Output

Student: Noah 91
Coordinate: 2.5 4

Pair is instantiated with a string/int combination for the student and two float64 fields for the coordinate. Field accesses preserve their declared types.

• The type argument list is part of the instantiated type, not optional decoration.
• Different type parameters are not automatically convertible to one another.

Add a generic Triple[A, B, C] struct and make one value holding a string, an int, and a bool.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Generic Structs in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.