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Clavin June
Clavin June

Posted on • Originally published at clavinjune.dev on

Construct Golang Struct Using Optional Function

Sunday Snippet #5 construct golang struct using optional function

Using optional function to allow user optionally set attributes

package main

import (
    "bytes"
    "encoding/json"
    "fmt"
)

// ExampleOptFunc sets Example's optional attribute
type ExampleOptFunc func(*Example)

// WithAttr1 sets Example's OptionalAttr1 as true
func WithAttr1() ExampleOptFunc {
    return func(e *Example) {
        e.OptionalAttr1 = true
    }
}

// WithAttr2 sets Example's OptionalAttr2 as i
func WithAttr2(i int) ExampleOptFunc {
    return func(e *Example) {
        e.OptionalAttr2 = i
    }
}

// WithAttr3 sets Example's OptionalAttr3 as s
func WithAttr3(s string) ExampleOptFunc {
    return func(e *Example) {
        e.OptionalAttr3 = s
    }
}

// Example is an example struct with some optional attributes
type Example struct {
    Name          string `json:"name"`
    OptionalAttr1 bool   `json:"optional_attr1"`
    OptionalAttr2 int    `json:"optional_attr2"`
    OptionalAttr3 string `json:"optional_attr3"`
}

// NewExample creates Example ptr
// requires name
func NewExample(name string, opts ...ExampleOptFunc) *Example {
    e := &Example{
        Name: name,
    }

    for _, opt := range opts {
        opt(e)
    }

    return e
}

// String returns json-encoded string
func (e *Example) String() string {
    var b bytes.Buffer
    enc := json.NewEncoder(&b)
    enc.SetIndent("", "  ")
    _ = enc.Encode(e)
    return b.String()
}

func main() {
    e := NewExample("example",
        WithAttr1(),
        WithAttr2(100),
        WithAttr3("testing"))

    fmt.Println(e)
    // {
    //   "name": "example",
    //   "optional_attr1": true,
    //   "optional_attr2": 100,
    //   "optional_attr3": "testing"
    // }
}
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