full snippet for the earthquakes compile type assertions

full-snippet.go

package main

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

func main() {
	jsonOfCoordinates := []string{
		"[10.84, 482.118, 45000]",
		"[45.84, 99.118]",
		"[-54, 10.84, 48218, 45000]",
	}

	for i, jsonStr := range jsonOfCoordinates {
		c := new(Coordinate)
		if err := json.Unmarshal([]byte(jsonStr), c); err != nil {
			log.Fatal(err)
		}

		fmt.Printf("#%d: Latitude: %f Longitude: %f Depth: %f\n", i, c.Latitude, c.Longitude, c.Depth)
	}
}

type Coordinate struct {
	Latitude  float32 `json:"latitude"`
	Longitude float32 `json:"longitude"`
	Depth     float32 `json:"depth"`
}

var (
	lBrace = []byte("[")
	rBrace = []byte("]")
	comma  = []byte(",")
)

var _ json.Unmarshaler = (*Coordinate)(nil)

func (c *Coordinate) UnmarshalJSON(b []byte) error {
	b = bytes.TrimSpace(b)
	b = bytes.TrimPrefix(b, lBrace)
	b = bytes.TrimSuffix(b, rBrace)

	splits := bytes.Split(b, comma)
	var cleaned [][]byte
	for _, split := range splits {
		cleaned = append(cleaned, bytes.TrimSpace(split))
	}

	ptrsToSet := [...]*float32{
		0: &c.Longitude,
		1: &c.Latitude,
		2: &c.Depth,
	}

	for i, ptr := range ptrsToSet {
		if i >= len(cleaned) { // Done receiving values
			break
		}

		f64, err := strconv.ParseFloat(string(cleaned[i]), 32)
		if err != nil {
			return err
		}
		*ptr = float32(f64)
	}
	return nil
}