goava

Goava is a set of libraries based on draft version of Go 2 generics.

Read the blog post about this project

It's not ready for production or even development use.

Bugs found while working on this project:

• 39834
• 39839
• 39853
• 39878

Read more about the draft design of Go Generics: The Next Step for Generics

Table Of Contents

• Stream(T)
• Result(T)

Stream(T)

Initialize stream

Of([]int{1, 2, 3, 4})

or

Of([]string{"q", "w", "e"})

Filtering a stream

Let's get rid of some numbers:

stream.
    Of([]int{1, 2, 3, 4, 5}).
    Filter(func(x int) bool {
        return x%2 == 0
    }).
    Slice()

Mapping stream of A to stream of B

Let's get rid of some numbers

stream.Map(
    stream.Of([]int{1, 2}),
    func(x int) string { return fmt.Sprint(x) },
).Slice()

Matching

• Stream(Type).AnyMatch(func(Type) bool) returns true if any of elements in stream match given predicate
• Stream(Type).NoneMatch(func(Type) bool) returns true if none of elements in stream match given predicate
• Stream(Type).AllMatch(func(Type) bool) returns true if all of elements in stream match given predicate

Collecting Stream(Type) to a map[Key]Value

Define a stream of movies with name and score that users gave:

items := stream.Of(
    []MovieVote{
        {Name: "A", Score: 1},
        {Name: "A", Score: 2},
        {Name: "B", Score: 9},
        {Name: "B", Score: 10},
        {Name: "B", Score: 8},
        {Name: "C", Score: 7},
        {Name: "C", Score: 8},
        {Name: "C", Score: 7},
    },
)

Now let's collect create a hashmap where key is a name of movie and value is sum of scores:

result := stream.Collect(
    items,
    collector.ToMap(MovieVote, string, int)(
        func(movie MovieVote) (string, int) {
            return movie.Name, movie.Score
        },
        func(total, score int) int {
            return total + score
        },
    ),
)

The first argument to ToMap is a mapper, it receives original item and returns a tuple of key and value. The second argument to ToMap is a accumulator, it current value and new value given by mapper or during combining parallel stream chunks. Yes, parallel.

A stream can be switched to parallel mode, so mapping and accumulation will be done in concurrent mode.

items = items.Parallel()

A stream can be switched back to sequential mode by calling Sequential() function.

Result(T)

The main goal was to bring Rust's powerful Result<T> to Go. Unfortunately, it can't be ported completely due to lack of pattern matching in Go.

The only possible way was to use channels and select {}, but it would be too complicated and it would be just an imitation.

Methods implemented so far:

IsOk() bool

IsOk returns true if the result is Ok.

IsErr() bool

IsErr returns true if the result is Err.

And(res Result(T)) Result(T)

And returns res if the result is Ok, otherwise returns the Err value of self.

OrElse(func() Result(T)) Result(T)

OrElse Calls fn if the result is Err, otherwise returns the Ok value of self.

Or(res Result(T)) Result(T)

Returns res if the result is Err, otherwise returns the Ok value of self.

Ok() T

OK returns the contained Ok value. Panics if the result is an Err

Err() error

Err returns the contained Err value. Panics if the result is Ok

OkOr(T) T

OkOr returns the contained Ok value or a provided default.

OkOrElse(fn func() T) T

OkOrElse returns the contained Ok value or calls provided fn.

Expect(msg string) T

Expect returns the contained Ok value. Panics if the value is an Err, with a panic message including the passed message, and the content of the Err.

ExpectErr(msg string) error

Expect returns the contained Err value. Panics if the value is an Ok, with a panic message including the passed message, and the content of the Ok.

Example

func Success() Result(int) {
    return Ok(42)
}

func Fail() Result(int) {
    return Err(int)(errors.New("failure"))
}

func main() {
    fmt.Println(Fail().OrElse(Success))

    result := Success().And(Fail())
    if result.IsOk() {
        fmt.Println("it's ok", result.Ok())
    } else {
        fmt.Println("it's not ok, but here is default value:", result.OkOr(1))
    }
}

License

MIT