From fe3f5b1fec1802ff5dea7faebafe69e07d22c80a Mon Sep 17 00:00:00 2001
From: Heshan Padmasiri <heshanp@wso2.com>
Date: Mon, 7 Oct 2024 14:13:28 +0530
Subject: [PATCH] Update error intersection

---
 .../error_type_intersection.bal               | 66 +++++++++++--------
 .../error_type_intersection.md                |  2 +-
 .../error_type_intersection.out               |  4 +-
 3 files changed, 43 insertions(+), 29 deletions(-)

diff --git a/examples/error-type-intersection/error_type_intersection.bal b/examples/error-type-intersection/error_type_intersection.bal
index cd904bcb04..cd0c1d7992 100644
--- a/examples/error-type-intersection/error_type_intersection.bal
+++ b/examples/error-type-intersection/error_type_intersection.bal
@@ -1,33 +1,47 @@
 import ballerina/io;
 
-type IOError distinct error;
+type InputErrorDetail record {|
+    int|string value;
+|};
 
-type FileErrorDetail record {
-    string filename;
-};
+type NumericErrorDetail record {|
+    int|float value;
+|};
 
-// The `FileIOError` type is defined as an intersection type using the `&` notation.
-// It is the intersection of two error types: `IOError` and `error<FileErrorDetail>`.
-// An error value belongs to this type if and only if it belongs to both `IOError` 
-// and `error<FileErrorDetail>`.
-type FileIOError IOError & error<FileErrorDetail>;
+type InputError error<InputErrorDetail>;
+
+type NumericError error<NumericErrorDetail>;
+
+type DistinctInputError distinct error<InputErrorDetail>;
+
+type DistinctNumericError distinct error<NumericErrorDetail>;
+
+// NumericInputError has detail type, record {| int value |}
+type NumericInputError InputError & NumericError;
+
+// DistinctNumericInputError has type ids of both DistinctInputError and DistinctNumericError
+type DistinctNumericInputError DistinctInputError & DistinctNumericError;
+
+function createNumericInputError(int value) returns NumericInputError {
+    return error("Numeric input error", value = value);
+}
+
+function createDistinctNumericInputError(int value) returns DistinctNumericInputError {
+    return error("Distinct numeric input error", value = value);
+}
 
 public function main() {
-    // In order to create an error value that belongs to `FileIOError`, the `filename`
-    // detail field must be provided.
-    FileIOError fileIOError = error("file not found", filename = "test.txt");
-
-    // `fileIOError` belongs to both `IOError` and `error<FileErrorDetail>`.
-    io:println(fileIOError is IOError);
-    io:println(fileIOError is error<FileErrorDetail>);
-
-    // An `IOError` value will not belong to `FileIOError` if it doesn't belong to
-    // `error<FileErrorDetail>`.
-    IOError ioError = error("invalid input");
-    io:println(ioError is FileIOError);
-
-    // Similarly, an error value belonging to `error<FileErrorDetail>` will not belong 
-    // to `FileIOError` if it doesn't belong to `IOError`.
-    error<FileErrorDetail> fileError = error("cannot remove file", filename = "test.txt");
-    io:println(fileError is FileIOError);
+    NumericInputError e1 = createNumericInputError(5);
+    // e1 belong to InputError since it's detail type is a subtype of InputErrorDetail
+    io:println(e1 is InputError);
+
+    // e1 doesn't belong to DistinctInputError since it doesn't have the type id of DistinctInputError
+    io:println(e1 is DistinctInputError);
+
+    DistinctNumericInputError e2 = createDistinctNumericInputError(5);
+    // e2 belong to InputError since it's detail type is a subtype of InputErrorDetail
+    io:println(e2 is InputError);
+
+    // e2 belong to DistinctInputError since it's type id set include the type id of DistinctInputError
+    io:println(e2 is DistinctInputError);
 }
diff --git a/examples/error-type-intersection/error_type_intersection.md b/examples/error-type-intersection/error_type_intersection.md
index 2b65eb1bb1..8493c9da00 100644
--- a/examples/error-type-intersection/error_type_intersection.md
+++ b/examples/error-type-intersection/error_type_intersection.md
@@ -1,6 +1,6 @@
 # Type intersection for error types
 
-You can define an error type that is both a subtype of a `distinct` error type and has additional constraints on the detail fields using intersection types.
+If you intersect two `error` types, the resulting type's detail type is the intersection of the detail types of both types. Furthermore, if any of the types being intersected is a distinct type, then the resultant type's type ID set includes all the type IDs of that type.
 
 ::: code error_type_intersection.bal :::
 
diff --git a/examples/error-type-intersection/error_type_intersection.out b/examples/error-type-intersection/error_type_intersection.out
index e315509605..20c659f272 100644
--- a/examples/error-type-intersection/error_type_intersection.out
+++ b/examples/error-type-intersection/error_type_intersection.out
@@ -1,5 +1,5 @@
 $ bal run error_type_intersection.bal
 true
-true
-false
 false
+true
+true