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atdj: generate wrapper classes for top-level list aliases (#500)
* atdj: generate wrapper classes for top-level list aliases Java has no type aliases, so 'type items = item list' previously caused an error. We now generate a class Items implementing Atdj with: - a no-arg constructor (empty list) - a constructor from ArrayList<Item> - a constructor from a JSON string - a package-private constructor from JSONArray (analogous to the JSONObject constructor generated for records) - toJsonBuffer / toJson - a public 'value' field of type ArrayList<Item> The assign function is also updated so that list aliases used as record fields or sum-variant payloads are deserialized via 'new Items(jsonArray)' rather than triggering the inline ArrayList-building loop. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * Update CHANGES.md for atdj list alias support Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * atdj: cast keys().next() to String for newer org.json JSONObject.keys() returns Iterator<Object> in newer versions of org.json, causing a compile error. The returned key is always a String in practice, so a cast is safe. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
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‎CHANGES.md‎

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@@ -1,3 +1,14 @@
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4.1.1 (unreleased)
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------------------
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* atdj: Top-level list aliases such as `type items = item list` are now
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supported. A wrapper class (e.g. `Items`) implementing `Atdj` is generated
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with the same interface as record classes: a no-arg constructor, a
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constructor from `ArrayList<T>`, a constructor from a JSON string, a
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package-private constructor from `JSONArray`, `toJsonBuffer`, `toJson`,
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and a public `value` field of type `ArrayList<T>`. List aliases used as
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record fields or sum-variant payloads are also handled correctly.
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4.1.0 (2026-04-11)
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------------------
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‎atdj/src/atdj_helper.ml‎

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@@ -47,7 +47,7 @@ class Util {
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JSONObject obj = (JSONObject)value;
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if (obj.length() != 1)
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throw new JSONException(\"Expected single-key object for sum type\");
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return obj.keys().next();
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return (String) obj.keys().next();
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}
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else throw new JSONException(\"Cannot extract type\");
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}

‎atdj/src/atdj_trans.ml‎

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@@ -67,6 +67,9 @@ let rec assign env opt_dst src java_ty atd_ty indent =
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sprintf "new %s(%s)" java_ty src
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| Record _ ->
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sprintf "new %s(%s)" java_ty src
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| List _ when not (String.contains java_ty '<') ->
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(* Named list alias class - use the JSONArray constructor *)
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sprintf "new %s(%s)" java_ty src
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| Name (_, (_, ty, _), _) ->
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(match Atd.Type_name.basename ty with
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| "bool" | "int" | "float" | "string" -> src
@@ -81,18 +84,22 @@ let rec assign env opt_dst src java_ty atd_ty indent =
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| Record _ ->
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sprintf "%s%s = new %s(%s);\n" indent dst java_ty src
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| List (_, sub_ty, _) ->
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let java_sub_ty = (*ahem*) extract_from_edgy_brackets java_ty in
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let sub_expr = assign env None "_tmp" java_sub_ty sub_ty "" in
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if String.contains java_ty '<' then
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let java_sub_ty = (*ahem*) extract_from_edgy_brackets java_ty in
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let sub_expr = assign env None "_tmp" java_sub_ty sub_ty "" in
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sprintf "%s%s = new %s();\n" indent dst java_ty
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^ sprintf "%sfor (int _i = 0; _i < %s.length(); ++_i) {\n" indent src
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sprintf "%s%s = new %s();\n" indent dst java_ty
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^ sprintf "%sfor (int _i = 0; _i < %s.length(); ++_i) {\n" indent src
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^ sprintf "%s %s _tmp = %s.%s(_i);\n" indent
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(json_of_atd env sub_ty) src (get env sub_ty false)
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^ sprintf "%s %s _tmp = %s.%s(_i);\n" indent
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(json_of_atd env sub_ty) src (get env sub_ty false)
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^ sprintf "%s %s.add(%s);\n" indent
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dst sub_expr
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^ sprintf "%s}\n" indent
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^ sprintf "%s %s.add(%s);\n" indent
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dst sub_expr
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^ sprintf "%s}\n" indent
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else
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(* Named list alias class - use the JSONArray constructor *)
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sprintf "%s%s = new %s(%s);\n" indent dst java_ty src
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| Name (_, (_, ty, _), _) ->
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(match Atd.Type_name.basename ty with
@@ -315,11 +322,90 @@ and trans_outer env (def : A.type_def) =
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trans_sum name env (loc, v, a)
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| Record (loc, v, a) ->
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trans_record name env (loc, v, a)
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| Name (_, (_, _name, _), _) ->
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(* Don't translate primitive types at the top-level *)
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env
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| List (_, sub_ty, _) ->
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trans_list_alias name env sub_ty
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| Name (_, (_, _name, _), _) as ty ->
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(match norm_ty env ty with
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| List (_, sub_ty, _) -> trans_list_alias name env sub_ty
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| _ -> (* Don't translate primitive types at the top-level *) env)
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| x -> type_not_supported x
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(* Translation of a top-level list alias, e.g. 'type items = item list'.
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* Since Java has no type aliases, we generate a class Items that wraps an
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* ArrayList and provides the same JSON interface as record classes.
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*)
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and trans_list_alias my_name env sub_atd_ty =
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let class_name = Atdj_names.to_class_name my_name in
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let (java_sub_ty, env) = trans_inner env sub_atd_ty in
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let json_sub_ty = json_of_atd env sub_atd_ty in
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let get_method = get env sub_atd_ty false in
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let sub_expr = assign env None "_tmp" java_sub_ty sub_atd_ty "" in
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let ctor_body =
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sprintf " for (int _i = 0; _i < ja.length(); ++_i) {\n"
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^ sprintf " %s _tmp = ja.%s(_i);\n" json_sub_ty get_method
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^ sprintf " value.add(%s);\n" sub_expr
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^ sprintf " }\n"
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in
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let to_json_body =
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sprintf " _out.append(\"[\");\n"
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^ sprintf " for (int i = 0; i < value.size(); ++i) {\n"
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^ to_string env "value.get(i)" sub_atd_ty " "
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^ sprintf " if (i < value.size() - 1)\n"
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^ sprintf " _out.append(\",\");\n"
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^ sprintf " }\n"
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^ sprintf " _out.append(\"]\");\n"
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in
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let out = open_class env class_name in
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fprintf out "\
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public class %s implements Atdj {
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/**
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* Construct a fresh empty list.
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*/
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public %s() {
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value = new java.util.ArrayList<%s>();
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}
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/**
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* Construct from an existing list.
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*/
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public %s(java.util.ArrayList<%s> arr) {
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value = arr;
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}
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/**
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* Construct from a JSON string.
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*/
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public %s(String s) throws JSONException {
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this(new JSONArray(s));
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}
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%s(JSONArray ja) throws JSONException {
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value = new java.util.ArrayList<%s>();
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%s }
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public void toJsonBuffer(StringBuilder _out) throws JSONException {
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%s }
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public String toJson() throws JSONException {
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StringBuilder out = new StringBuilder(128);
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toJsonBuffer(out);
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return out.toString();
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}
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public java.util.ArrayList<%s> value;
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}
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"
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class_name
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class_name java_sub_ty
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class_name java_sub_ty
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class_name
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class_name java_sub_ty
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ctor_body
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to_json_body
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java_sub_ty;
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close_out out;
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env
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(* Translation of sum types. For a sum type
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*
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* type ty = Foo | Bar of whatever

‎atdj/test/com/mylife/test/dune‎

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B.java
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ComplexRecord.java
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E.java
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Items.java
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RecordWithDefaults.java
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SampleSum.java
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Shape.java

‎atdj/test/dune‎

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(package atdj)
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(action (diff expected/E.java com/mylife/test/E.java)))
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(rule
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(alias runtest)
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(package atdj)
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(action (diff expected/Items.java com/mylife/test/Items.java)))
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(rule
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(alias runtest)
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(package atdj)

‎atdj/test/expected/Items.java‎

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// Automatically generated; do not edit
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package com.mylife.test;
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import org.json.*;
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public class Items implements Atdj {
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/**
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* Construct a fresh empty list.
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*/
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public Items() {
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value = new java.util.ArrayList<SimpleRecord>();
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}
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/**
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* Construct from an existing list.
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*/
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public Items(java.util.ArrayList<SimpleRecord> arr) {
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value = arr;
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}
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/**
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* Construct from a JSON string.
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*/
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public Items(String s) throws JSONException {
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this(new JSONArray(s));
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}
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Items(JSONArray ja) throws JSONException {
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value = new java.util.ArrayList<SimpleRecord>();
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for (int _i = 0; _i < ja.length(); ++_i) {
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JSONObject _tmp = ja.getJSONObject(_i);
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value.add(new SimpleRecord(_tmp));
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}
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}
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public void toJsonBuffer(StringBuilder _out) throws JSONException {
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_out.append("[");
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for (int i = 0; i < value.size(); ++i) {
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value.get(i).toJsonBuffer(_out);
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if (i < value.size() - 1)
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_out.append(",");
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}
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_out.append("]");
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}
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public String toJson() throws JSONException {
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StringBuilder out = new StringBuilder(128);
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toJsonBuffer(out);
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return out.toString();
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}
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public java.util.ArrayList<SimpleRecord> value;
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}

‎atdj/test/expected/Util.java‎

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@@ -20,7 +20,7 @@ else if (value instanceof JSONObject) {
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JSONObject obj = (JSONObject)value;
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if (obj.length() != 1)
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throw new JSONException("Expected single-key object for sum type");
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return obj.keys().next();
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return (String) obj.keys().next();
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}
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else throw new JSONException("Cannot extract type");
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}

‎atdj/test/test.atd‎

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@@ -48,6 +48,10 @@ type simple_record = { ?o : bool option }
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type a = [ A of b list ]
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type b = [ B ]
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(* Type alias for a list - Java doesn't support type aliases, so we generate
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a wrapper class with the same JSON interface as record classes. *)
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type items = simple_record list
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(*
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Sum type using the object encoding: {"Constructor": payload}
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instead of the default array encoding: ["Constructor", payload].

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