Go functions dot notation

Question

I want to build this:

finalResult, err := Function1(whatever type)
    .Function2(whatever type)
    .Function3(whatever type)

Something similar to promises in javascript but not necessarily the same concepts. Or similar to nested methods in Java. I just pretend avoid more code for the same tasks.

I don't want to do this :

result, err := new(Function1(whatever type)) //or *Function1(whatever type)
if err != nil {...}
result1, err := result.Function2(whatever type)
if err != nil {...}
finalResult, err := result1.Function3(whatever type)
if err != nil {...}

I've been trying with several options with structs and interfaces but I can't get any result.

My apology if I have a mistake in my grammar. I'm not still so good with my skill English.

Thanks,

David

Answer 1

I think you mean the Fluent API design pattern. You return the same Object, or struct in Go, over and over.

This pattern does not allow you to return a tuple, or multiple return types though. You can only return one object.

https://play.golang.org/p/9PceZwi1a3

package main

import (
    "fmt"
)

type Object struct {
    Value string
    Error error
}

func (o *Object) Before(s string) *Object {
    o.Value = s + o.Value
    // add an error if you like
    // o.Error = error.New(...)
    return o
}

func (o *Object) After(s string) *Object {
    // could check for errors too
    if o.Error != nil {
        o.Value = o.Value + s
    }
    return o
}

func main() {
    x := Object{}

    x.
        Before("123").
        After("456").
        After("789").
        Before("0")

    if x.Error != nil {
        // handle error
    }
    fmt.Println(x.Value)
}

Edit: sberry's answer had a good idea. Add an Error state on the Object struct itself which could allow u to check for errors in each func call.

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