feat: remove null properties encoder and decoder

Signed-off-by: Aleksei Gurianov <[email protected]>

README.md

@@ -60,11 +60,99 @@ pub fn main() {
   )
   // Encode the Feature to GeoJSON
   |> gleojson.GeoFeature
-  |> gleojson.encode_geojson(gleojson.properties_null_encoder)
+  |> gleojson.encode_geojson(fn(_) { json.null() })
   |> json.to_string
 }
 ```
 
+Decoding GeoJSON objects is also straightforward:
+
+```gleam:./test/examples/decode.gleam
+import decode/zero
+import examples/to_dynamic_decoder.{to_dynamic_decoder}
+import gleam/bool
+import gleam/float
+import gleam/int
+import gleam/io
+import gleam/json
+import gleam/option
+import gleojson
+
+// Define custom properties type for your features
+pub type ParkProperties {
+  ParkProperties(
+    name: String,
+    area_sq_km: Float,
+    year_established: Int,
+    is_protected: Bool,
+  )
+}
+
+// Define decoder for your custom properties
+fn park_properties_decoder() {
+  use name <- zero.field("name", zero.string)
+  use area_sq_km <- zero.field("area_sq_km", zero.float)
+  use year_established <- zero.field("year_established", zero.int)
+  use is_protected <- zero.field("is_protected", zero.bool)
+  ParkProperties(name:, area_sq_km:, year_established:, is_protected:)
+  |> zero.success
+}
+
+pub fn main() {
+  // Example GeoJSON string representing a national park
+  let json_string =
+    "{
+    \"type\": \"Feature\",
+    \"geometry\": {
+      \"type\": \"Point\",
+      \"coordinates\": [-119.5383, 37.8651]
+    },
+    \"properties\": {
+      \"name\": \"Yosemite National Park\",
+      \"area_sq_km\": 3029.87,
+      \"year_established\": 1890,
+      \"is_protected\": true
+    },
+    \"id\": \"yosemite\"
+  }"
+
+  // Decode the JSON string into a GeoJSON object
+  let decoded =
+    json.decode(
+      from: json_string,
+      using: to_dynamic_decoder(
+        gleojson.geojson_decoder(park_properties_decoder()),
+      ),
+    )
+
+  // Handle the decoded result
+  case decoded {
+    Ok(geojson) -> {
+      case geojson {
+        gleojson.GeoFeature(feature) -> {
+          case feature.properties {
+            option.Some(ParkProperties(name, area, year, is_protected)) -> {
+              io.println(
+                "Decoded " <> name <> ", established in " <> int.to_string(year),
+              )
+              io.println(
+                "Area: "
+                <> float.to_string(area)
+                <> " sq km, Protected: "
+                <> bool.to_string(is_protected),
+              )
+            }
+            option.None -> io.println("Feature has no properties")
+          }
+        }
+        _ -> io.println("Decoded a different type of GeoJSON object")
+      }
+    }
+    Error(_error) -> io.println("Failed to decode")
+  }
+}
+```
+
 For more advanced usage, including custom properties and decoding, see the [documentation](https://hexdocs.pm/gleojson).
 
 ## Development

src/gleojson.gleam

@@ -350,8 +350,8 @@ fn featurecollection_decoder(properties_decoder: zero.Decoder(properties)) {
 /// }
 /// ```
 ///
-/// Note: This function expects a valid GeoJSON structure. Invalid or incomplete
-/// GeoJSON data will result in a decode error.
+/// Note: This function expects a valid GeoJSON structure.
+/// Invalid or incomplete GeoJSON data will result in a decode error.
 pub fn geojson_decoder(properties_decoder: zero.Decoder(properties)) {
   use type_str <- zero.then(type_decoder())
   case type_str {
@@ -363,22 +363,6 @@ pub fn geojson_decoder(properties_decoder: zero.Decoder(properties)) {
   }
 }
 
-/// Encodes null properties for Features and FeatureCollections.
-///
-/// This is a utility function that can be used as the `properties_encoder`
-/// argument for `encode_geojson` when you don't need to encode any properties.
-pub fn properties_null_encoder(_props) {
-  json.null()
-}
-
-/// Decodes null properties for Features and FeatureCollections.
-///
-/// This is a utility function that can be used as the `properties_decoder`
-/// argument for `geojson_decoder` when you don't need to decode any properties.
-pub fn properties_null_decoder() {
-  zero.success(Ok(Nil))
-}
-
 /// Creates a 2D Position object from longitude and latitude values.
 ///
 /// This function is a convenience helper for creating a Position object

test/examples/decode.gleam

@@ -0,0 +1,83 @@
+import decode/zero
+import examples/to_dynamic_decoder.{to_dynamic_decoder}
+import gleam/bool
+import gleam/float
+import gleam/int
+import gleam/io
+import gleam/json
+import gleam/option
+import gleojson
+
+// Define custom properties type for your features
+pub type ParkProperties {
+  ParkProperties(
+    name: String,
+    area_sq_km: Float,
+    year_established: Int,
+    is_protected: Bool,
+  )
+}
+
+// Define decoder for your custom properties
+fn park_properties_decoder() {
+  use name <- zero.field("name", zero.string)
+  use area_sq_km <- zero.field("area_sq_km", zero.float)
+  use year_established <- zero.field("year_established", zero.int)
+  use is_protected <- zero.field("is_protected", zero.bool)
+  ParkProperties(name:, area_sq_km:, year_established:, is_protected:)
+  |> zero.success
+}
+
+pub fn main() {
+  // Example GeoJSON string representing a national park
+  let json_string =
+    "{
+    \"type\": \"Feature\",
+    \"geometry\": {
+      \"type\": \"Point\",
+      \"coordinates\": [-119.5383, 37.8651]
+    },
+    \"properties\": {
+      \"name\": \"Yosemite National Park\",
+      \"area_sq_km\": 3029.87,
+      \"year_established\": 1890,
+      \"is_protected\": true
+    },
+    \"id\": \"yosemite\"
+  }"
+
+  // Decode the JSON string into a GeoJSON object
+  let decoded =
+    json.decode(
+      from: json_string,
+      using: to_dynamic_decoder(
+        gleojson.geojson_decoder(park_properties_decoder()),
+      ),
+    )
+
+  // Handle the decoded result
+  case decoded {
+    Ok(geojson) -> {
+      case geojson {
+        gleojson.GeoFeature(feature) -> {
+          case feature.properties {
+            option.Some(ParkProperties(name, area, year, is_protected)) -> {
+              io.println(
+                "Decoded " <> name <> ", established in " <> int.to_string(year),
+              )
+              io.println(
+                "Area: "
+                <> float.to_string(area)
+                <> " sq km, Protected: "
+                <> bool.to_string(is_protected),
+              )
+            }
+            option.None -> io.println("Feature has no properties")
+          }
+        }
+        _ -> io.println("Decoded a different type of GeoJSON object")
+      }
+    }
+    Error(_error) -> io.println("Failed to decode")
+  }
+}

test/examples/encode.gleam

@@ -13,6 +13,6 @@ pub fn main() {
   )
   // Encode the Feature to GeoJSON
   |> gleojson.GeoFeature
-  |> gleojson.encode_geojson(gleojson.properties_null_encoder)
+  |> gleojson.encode_geojson(fn(_) { json.null() })
   |> json.to_string
 }

test/examples/to_dynamic_decoder.gleam

@@ -0,0 +1,6 @@
+import decode/zero.{type Decoder}
+import gleam/dynamic.{type Dynamic}
+
+pub fn to_dynamic_decoder(zero_decoder: Decoder(a)) {
+  fn(dynamic_value: Dynamic) { zero.run(dynamic_value, zero_decoder) }
+}

test/gleojson_test.gleam

@@ -1,5 +1,6 @@
 import birdie
 import decode/zero
+import examples/decode
 import examples/encode
 import gleam/dynamic
 import gleam/json
@@ -134,8 +135,8 @@ pub fn point_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "point_encode_decode",
   )
 }
@@ -151,8 +152,8 @@ pub fn multipoint_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "multipoint_encode_decode",
   )
 }
@@ -168,8 +169,8 @@ pub fn linestring_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "linestring_encode_decode",
   )
 }
@@ -189,8 +190,8 @@ pub fn polygon_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "polygon_encode_decode",
   )
 }
@@ -220,8 +221,8 @@ pub fn multipolygon_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "multipolygon_encode_decode",
   )
 }
@@ -240,8 +241,8 @@ pub fn geometrycollection_encode_decode_test() {
 
   assert_encode_decode(
     geojson,
-    gleojson.properties_null_encoder,
-    gleojson.properties_null_decoder(),
+    fn(_) { json.null() },
+    zero.success(Nil),
     "geometrycollection_encode_decode",
   )
 }
@@ -344,3 +345,8 @@ pub fn example_test() {
   |> dynamic.classify()
   |> should.equal("String")
 }
+
+pub fn example_decode_test() {
+  decode.main()
+  |> should.equal(Nil)
+}