go-tuple: Generic tuples for Go 1.18+.

Go 1.18+ tuple implementation.

Use tuples to store 1 or more values without needing to write a custom struct.

tup := tuple.New2(5, "hi!")
fmt.Println(tup.V1) // Outputs 5.
fmt.Println(tup.V2) // Outputs "hi!".

Tuples come in various sizes, from 1 to 9 elements.

longerTuple := tuple.New5("this", "is", "one", "long", "tuple")

Tuples can be used as slice or array items, map keys or values, and as channel payloads:

// Map holding tuples.
tupInMap := make(map[tuple.T2[string, string]]Person)
tupInMap[tuple.New2("John", "Doe")] = Person{
	FirstName: "John",
	LastName: "Doe",
	// ...
}

// Channel holding tuples.
tupInChan := make(chan tuple.T2[string, error])
go func() {
	defer close(tupInChan)
	tupInChan <- tuple.New2(os.Getwd())
}()
fmt.Print(<-tupInChan)

Features

Create tuples from function calls

func vals() (int, string) {
    return 5, "hi!"
}

func main() {
    tup := tuple.New2(vals())
    fmt.Println(tup.V1)
    fmt.Println(tup.V2)
}

Forward tuples as function arguments

func main() {
    tup := tuple.New2(5, "hi!")
    printValues(tup.Values())
}

func printValues(a int, b string) {
    fmt.Println(a)
    fmt.Println(b)
}

Access tuple values

tup := tuple.New2(5, "hi!")
a, b := tup.Values()

JSON Marshalling

Tuples are marshalled and unmarshalled as JSON arrays.

type User struct {
	Name string `json:"name"`
	Age  int    `json:"age,omitempty"`
}

type MyJSON struct {
	Users []tuple.T2[string, User] `json:"users"`
}

func main() {
	data := MyJSON{
		Users: []tuple.T2[string, User]{
			tuple.New2("foo", User{Name: "foo", Age: 42}),
			tuple.New2("bar", User{Name: "bar", Age: 21}),
			tuple.New2("baz", User{Name: "baz"}),
		},
	}

	marshalled, _ := json.Marshal(data)
	fmt.Printf("%s\n", string(marshalled))
	// Outputs: {"users":[["foo",{"name":"foo","age":42}],["bar",{"name":"bar","age":21}],["baz",{"name":"baz"}]]}
}

Comparison

Tuples are compared from the first element to the last. For example, the tuple [1 2 3] is greater than [1 2 4] but less than [2 2 2].

fmt.Println(tuple.Equal3(tuple.New3(1, 2, 3), tuple.New3(3, 3, 3))) // false.
fmt.Println(tuple.LessThan3(tuple.New3(1, 2, 3), tuple.New3(3, 2, 1))) // true.

tups := []tuple.T3{
    tuple.New3("foo", 2, -23),
    tuple.New3("foo", 72, 15),
    tuple.New3("bar", -4, 43),
}
sort.Slice(tups, func (i, j int) {
    return tuple.LessThan3(tups[i], tups[j])
})

fmt.Println(tups) // [["bar", -4, 43], ["foo", 2, -23], ["foo", 72, 15]].

---

NOTE

In order to compare tuples, all tuple elements must match constraints.Ordered.

See Custom comparison in order to see how to compare tuples with arbitrary element values.

---

Comparison result

// Compare* functions return an OrderedComparisonResult value.
result := tuple.Compare3(tuple.New3(1, 2, 3), tuple.New3(3, 2, 1))

// OrderedComparisonResult values are wrapped integers.
fmt.Println(result) // -1

// OrderedComparisonResult expose various method to see the result
// in a more readable way.
fmt.Println(result.GreaterThan()) // false

Custom comparison

The package provides the CompareC comparison functions varation in order to compare tuples of complex comparable types.

For a type to be comparable, it must match the Comparable or Equalable constraints.

type Comparable[T any] interface {
	CompareTo(guest T) OrderedComparisonResult
}

type Equalable[T any] interface {
	Equal(guest T) bool
}

type person struct {
	name string
	age  int
}

func (p person) CompareTo(guest person) tuple.OrderedComparisonResult {
	if p.name < guest.name {
		return -1
	}
	if p.name > guest.name {
		return 1
	}
	return 0
}

func main() {
	tup1 := tuple.New2(person{name: "foo", age: 20}, person{name: "bar", age: 24})
	tup2 := tuple.New2(person{name: "bar", age: 20}, person{name: "baz", age: 24})

	fmt.Println(tuple.LessThan2C(tup1, tup2)) // true.
}

In order to call the complex types variation of the comparable functions, all tuple types must match the Comparable constraint.

While this is not ideal, this a known inconvenience given the current type parameters capabilities in Go. Some solutions have been porposed for this issue (lesser, for example, beatifully articulates the issue), but they still demand features that are not yet implemented by the language.

Once the language will introduce more convenient ways for generic comparisons, this package will adopt it.

Formatting

Tuples implement the Stringer and GoStringer interfaces.

fmt.Printf("%s\n", tuple.New2("hello", "world"))
// Output:
// ["hello" "world"]

fmt.Printf("%#v\n", tuple.New2("hello", "world"))
// Output:
// tuple.T2[string, string]{V1: "hello", V2: "world"}

Notes

The tuple code and test code are generated by the scripts/gen/main.go script.

Generation works by reading tuple.tpl and tuple_test.tpl using Go's text/template engine. tuple.tpl and tuple_test.tpl contain the templated content of a generic tuple class, with variable number of elements.

Contributing

Please feel free to contribute to this project by opening issues or creating pull-requests. However, keep in mind that generic type features for Go are still in their early stages, so there might not be support from the language to your requested feature.

Also keep in mind when contributing to keep the compilation time and performance of this package fast.

Feel free to contact me at barw.code@gmail.com for questions or suggestions!