Field requires a type

2 files changed, 26 insertions, 9 deletions

diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index ff040db..fa1b69e 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -386,8 +386,13 @@ if javascript {
 ///    > field(from(123), "Hello")
 ///    Error(DecodeError(expected: "Map", found: "Int"))
 ///
-pub fn field(from value: Dynamic, named name: a) -> Result(Dynamic, DecodeError) {
-  decode_field(value, name)
+pub fn field(
+  from value: Dynamic,
+  named name: a,
+  of inner_type: Decoder(t),
+) -> Result(t, DecodeError) {
+  try value = decode_field(value, name)
+  inner_type(value)
 }
 
 if erlang {
diff --git a/test/gleam/dynamic_test.gleam b/test/gleam/dynamic_test.gleam
index ea40190..54eca0c 100644
--- a/test/gleam/dynamic_test.gleam
+++ b/test/gleam/dynamic_test.gleam
@@ -246,29 +246,41 @@ pub fn field_test() {
   map.new()
   |> map.insert("ok", 1)
   |> dynamic.from
-  |> dynamic.field("ok")
-  |> should.equal(Ok(dynamic.from(1)))
+  |> dynamic.field(named: "ok", of: dynamic.int)
+  |> should.equal(Ok(1))
+
+  map.new()
+  |> map.insert("ok", 1.0)
+  |> dynamic.from
+  |> dynamic.field(named: "ok", of: dynamic.float)
+  |> should.equal(Ok(1.0))
 
   map.new()
   |> map.insert("ok", 3)
   |> map.insert("error", 1)
   |> dynamic.from
-  |> dynamic.field("ok")
-  |> should.equal(Ok(dynamic.from(3)))
+  |> dynamic.field("ok", dynamic.int)
+  |> should.equal(Ok(3))
+
+  map.new()
+  |> map.insert("ok", 3)
+  |> dynamic.from
+  |> dynamic.field("ok", dynamic.float)
+  |> should.be_error
 
   map.new()
   |> dynamic.from
-  |> dynamic.field("ok")
+  |> dynamic.field("ok", dynamic.int)
   |> should.be_error
 
   1
   |> dynamic.from
-  |> dynamic.field("ok")
+  |> dynamic.field("ok", dynamic.int)
   |> should.be_error
 
   []
   |> dynamic.from
-  |> dynamic.field([])
+  |> dynamic.field("ok", dynamic.int)
   |> should.be_error
 }