example.go

// So, in order to unmarshal json easily with Go it's important to code Go structs that 
// follow the structure of the data you will receive. It might be a bit of extra coding
// up front, but I think it has some nice benefits since you can then can work with native
// structs and have type safety enforced.

// Keep in mind that this is an example so my naming might not be the best, but I hope it
// will be helpful to you anyways.

// I created the structs and their relationships based on the sample response from the API
// documentation you sent me, which is copied at the bottom for clarity.
// Feel free to reach out if any of this is confusing or I can help with anything else!

type MapsQuery struct {
  Status        string    `json:"status"`
  ErrorMessage  string    `json:"error_message"`
  Results       []Result  `json:"results"`
}

type Result struct {
  PlaceID           string             `json:"place_id"`
  FormattedAddress  string             `json:"formatted_address"`
  Types             []string           `json:"types"`
  AddressComponents []AddressComponent `json:"address_components"`
  Geometry          Geometry           `json:"geometry"`
}

type AddressComponent struct {
  LongName  string    `json:"long_name"`
  ShortName string    `json:"short_name"`
  Types     []string  `json:"types"`
}

type Geometry struct {
  LocationType  string              `json:"location_type"`
  Location      Location            `json:"location"`
  Viewport      map[string]Location `json:"viewport"`
}

type Location struct {
  Lat float64 `json:"lat"`
  Lon float64 `json:"lon"`
}


// This way, you can instanciate a maps query and unmarshal the response into it.
var queryResult MapsQuery
json.Unmarshal(yourResponseBody, queryResult)

// And then you have a Go struct filled up with everything in it, so you can manipulate it like this:

queryResult.Status //=> "OK"

queryResult.Results[0].PlaceID //=> "ChIJ2eUgeAK6j4ARbn5u_wAGqWA"

queryResult.Results[0].AddressComponents[0].LongName //=> "1600"

queryResult.Results[0].Geometry.Location.Lat //=> 37.4224764

queryResult.Results[0].Geometry.Viewport["northeast"].Lat //=> 37.4238253802915

// You can iterate throught the results as you would in normal Go code.
for _, result in queryResult.Results {
  // ...
}

// I made this example with the following sample response in mind, from the documentation:

`
{
   "results" : [
      {
         "address_components" : [
            {
               "long_name" : "1600",
               "short_name" : "1600",
               "types" : [ "street_number" ]
            },
            {
               "long_name" : "Amphitheatre Pkwy",
               "short_name" : "Amphitheatre Pkwy",
               "types" : [ "route" ]
            },
            {
               "long_name" : "Mountain View",
               "short_name" : "Mountain View",
               "types" : [ "locality", "political" ]
            },
            {
               "long_name" : "Santa Clara County",
               "short_name" : "Santa Clara County",
               "types" : [ "administrative_area_level_2", "political" ]
            },
            {
               "long_name" : "California",
               "short_name" : "CA",
               "types" : [ "administrative_area_level_1", "political" ]
            },
            {
               "long_name" : "United States",
               "short_name" : "US",
               "types" : [ "country", "political" ]
            },
            {
               "long_name" : "94043",
               "short_name" : "94043",
               "types" : [ "postal_code" ]
            }
         ],
         "formatted_address" : "1600 Amphitheatre Parkway, Mountain View, CA 94043, USA",
         "geometry" : {
            "location" : {
               "lat" : 37.4224764,
               "lng" : -122.0842499
            },
            "location_type" : "ROOFTOP",
            "viewport" : {
               "northeast" : {
                  "lat" : 37.4238253802915,
                  "lng" : -122.0829009197085
               },
               "southwest" : {
                  "lat" : 37.4211274197085,
                  "lng" : -122.0855988802915
               }
            }
         },
         "place_id" : "ChIJ2eUgeAK6j4ARbn5u_wAGqWA",
         "types" : [ "street_address" ]
      }
   ],
   "status" : "OK"
}
`

This was very useful, thanks! One thing that came up is that json.Unmarshal requires a pointer for its second argument, so I had to modify line 47 to json.Unmarshal(yourResponseBody, &queryResult) - then it worked fine.

In the end I'm not sure I would choose Golang to write this particular bit of code in again, but it was a fun exercise :)