Sushi: a series of Go utilities

Function

Function represents any generic transformation applied on a generic type T into another (or the same) type V. The transformation can generate an error, which is returned in output, as its declaration shows:

type Function[T any, V any] func(t T) (*V, error)

To implement a Function type you can simply so something like this:

func myfunc(input int) (*string, error) {
    if input < 10 {
        return nil, fmt.Errorf("input is less than 10!")
    } 
    output := fmt.Sprintf(" -- %d -- ", input-5)
    return &output, nil
}

Either

Either represents the result of an operation which can either be a successful result or an error as shown by its declaration:

type Either[V any] struct {
        result *V
        err    error
}

You can force the generation of an Either leaving aside any computation using these two utility methods:

successEither := functional.EitherFromResult[int](10)
failureEither := functional.EitherFromError[string](fmt.Error("error!"))

After a computation, you can check if an Either wraps a success result or an error through the following functions:

successEither.IsResult() // -> true
successEither.IsError()  // -> false

failureEither.IsResult() // -> false
failureEither.IsError()  // -> true

And then, you can get the result or the error accordingly:

result := successEither.getResult()
fmt.Println(*result)

err := failureEither.getError()
fmt.Println(err)

If you use the function GetResult() in presence of an error, the goroutine panics, so better check before attempting to get a result. If you want to get both the values from an Either you can:

result, err := failureEither.Get()

If you want to establish a fallback result in case of error you can use the following:

result := failureEither.GetOrElse("fallbackValue") // it will return a pointer to "fallbackValue"

Future

It is the implementation of an async task running on a different goroutine. It takes advantage of both Function and Either types. Future implementation is under goutils/functional package. To import it:

import (
    "github.com/gyozatech/sushi/functional"
)

To use a Future you need to define a Function which represents the task to be implemented asynchronously and the input to that task:

func task(input int) (*string, error) {
    if input < 10 {
        return nil, fmt.Errorf("input is less than 10!")
    } 
    output := fmt.Sprintf(" -- %d -- ", input-5)
    return &output, nil
}

func main() {
    // create and process a task asynchronously
    future := functional.ProcessAsync(task, 10)
    // block the current goroutine until the result is ready
    either := future.WaitForResult()
    // get the result
    result := either.GetResult()
    fmt.Printf("%T : '%v' \n", result, *result)
}

You can execute heavy tasks in parallel by simply doing:

future1 := functional.ProcessAsync(task, 10)
future2 := functional.ProcessAsync(task, 100)
future3 := functional.ProcessAsync(task, 65)

res1, err1 := future1.WaitForResult().Get()
res2, err2 := future2.WaitForResult().Get()
res3, err3 := future3.WaitForResult().Get()

The function WaitForResult() is a blocking operation, so that the time to wait in the main goroutine is the max time among the executions of the three tasks.

You can also choose not to start the tasks directly this way:

// prepare the future without starting its execution
input := 10
future := functional.NewFuture(task, input)

// execute asynchronously
future.Process()

// wait and get the result
res, err := future.WaitForResult().Get()

---

Utils

EnrichContextWithValue and FetchContextValue

These are useful to enrich the conxtext and fetch values from it:

import 
(
    "github.com/gyozatech/sushi/utils"
    "context"
)
func LetsTry() {
    ctx := context.TODO()
    ctx = utils.EnrichContextWithValue(ctx, "name", "Alessandro")
    ctx = utils.EnrichContextWithValue(ctx, "age", 35)
    ctx = utils.EnrichContextWithValue(ctx, "subscribed", true)
    ctx = utils.EnrichContextWithValue(ctx, "book", Book{Title: "Jurassic Park", Author: "Michael Chricton"})

    var name *string = utils.FetchContextValue[string](ctx, "name")
    var age *int = utils.FetchContextValue[int](ctx, "age")
    var subscribed *bool = utils.FetchContextValue[bool](ctx, "subscribed")
    var book *Book = utils.FetchContextValue[Book](ctx, "book")
    var unexisting *string= utils.FetchContextValue[string](ctx, "unexisting")
}

IsEqual

Is equal is a strong utility to compare equalness, much more elastic than deepEqual:

import (
    "github.com/gyozatech/sushi/utils"
    "fmt"
)

func LetsTry() error {
    isEqual := utils.IsEqual([]*string{ "1", "2", "3"}, []uint16{ 1, 2, 3 })
    if !isEqual {
        return fmt.Errorf("They should be equal!")
    }
}

CollectResults

Allows you to collect all results of a function in a slice:

import (
    "github.com/gyozatech/sushi/utils"
    "fmt"
)

func GetUser(id string) (email string, subscribed bool, age int, err error) {
    // ...
    return "[email protected]", true, 35, nil
}

func LetsTry() error {
    age := CollectResults(GetUser("12345"))[2]
    fmt.Println("Age:", age)
}

ForEach

Allows you to apply a mutator over a slice

import (
    "github.com/gyozatech/sushi/functional"
    "fmt"
)

func LetsTry() {
    // output type
    type DB struct {
	    Type string
	    Version string
	}
	
    // input slice
	dbCodes := []string{"mysql-v8.5.6", "postgres-v5.3.1", "postgres-v4.2.4", "mysql-v11.2.3"}

    // mutator function from string to DB
    var fetchDBFromCode functional.Function[string, DB] = func(dbCode string) (*DB, error) {
	     split := strings.Split(dbCode, "-")
	     if len(split) != 2 {
	         return nil, fmt.Errorf("invalid DB version provided %s", dbCode)
	     }
	     return &DB{ Type: split[0], Version: split[1] }, nil
	}
	// apply mutator to every element of the initial slice with ForEach
	databases, err := functional.ForEach(dbCodes, fetchDBFromCode)
	if err != nil {
	    fmt.Printf("Error: %s \n", err.Error())
	} else {
	    fmt.Printf("%+v \n", databases)
	}
}

FindOne and FindMany

These two functions allow filtering a slice through a condition:

import (
    "github.com/gyozatech/sushi/utils"
)

func LetsTry() {

    type Book struct {
        ID int
        Title string
        Author string
    }

    books := []Book{
        {ID: 1, Title: "Jurassic Park", Author: "Michael Chricton"},
        {ID: 2, Title: "The Lost World", Author: "Michael Chricton"},
        {ID: 3, Title: "Relic", Author: "Preston & Child"},
    }

    jkBook := utils.FindOne(books, func(b Book) bool{
        return b.Title == "Jurassic Park"
    })

    chrictonBooks := utils.FindMany(books, func(b Book) bool{
        return b.Author == "Michael Chricton"
    })

    _ = jkBook
    _ = chrictonBooks

}