Merge pull request #223 from bytecodealliance/ydnar/result-ergonomics

cm: improve ergonomics of Result types

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 ### Added
 
 - `wit-bindgen-go` now accepts arguments that control the level of logging output on stderr. Verbose mode (`-v` or `--verbose`) will print informational log lines, warnings, and errors. Debug mode (`-vv` or `--debug`) will emit finer-grained debugging information. By default, `wit-bindgen-go` will print warnings or errors.
+- New method `(cm.Result).Result() (ok OK, err Err, isErr bool)` added to streamline common patterns using `result` types. It has a value receiver, allowing it to be chained off a function call that returns a `Result`, eliminating the need to declare a temporary variable. For example: `stream, err, isErr := stream.BlockingRead(n)`
 
 ### Fixed
 

cm/result.go

@@ -71,6 +71,16 @@ func (r *result[Shape, OK, Err]) Err() *Err {
 	return (*Err)(unsafe.Pointer(&r.data))
 }
 
+// Result returns (OK, zero value of Err, false) if r represents the OK case,
+// or (zero value of OK, Err, true) if r represents the error case.
+// This does not have a pointer receiver, so it can be chained.
+func (r result[Shape, OK, Err]) Result() (ok OK, err Err, isErr bool) {
+	if r.isErr {
+		return ok, *(*Err)(unsafe.Pointer(&r.data)), true
+	}
+	return *(*OK)(unsafe.Pointer(&r.data)), err, false
+}
+
 // This function is sized so it can be inlined and optimized away.
 func (r *result[Shape, OK, Err]) validate() {
 	var shape Shape

cm/result_test.go

@@ -17,6 +17,48 @@ type resulter[OK, Err any] interface {
 	IsErr() bool
 	OK() *OK
 	Err() *Err
+	Result() (OK, Err, bool)
+}
+
+func TestResultOKOrErr(t *testing.T) {
+	r1 := OK[Result[string, string, struct{}]]("hello")
+	if ok := r1.OK(); ok == nil {
+		t.Errorf("OK(): %v, expected non-nil OK", ok)
+	}
+	if err := r1.Err(); err != nil {
+		t.Errorf("Err(): %v, expected nil Err", err)
+	}
+
+	r2 := Err[Result[bool, struct{}, bool]](true)
+	if ok := r2.OK(); ok != nil {
+		t.Errorf("OK(): %v, expected nil OK", ok)
+	}
+	if err := r2.Err(); err == nil {
+		t.Errorf("Err(): %v, expected non-nil Err", err)
+	}
+}
+
+func TestResultResult(t *testing.T) {
+	ok, err, isErr := OK[Result[string, string, int]]("hello").Result()
+	if got, want := ok, "hello"; got != want {
+		t.Errorf("Result(): ok = %v; expected %v", got, want)
+	}
+	if got, want := err, 0; got != want {
+		t.Errorf("Result(): err = %v; expected %v", got, want)
+	}
+	if got, want := isErr, false; got != want {
+		t.Errorf("Result(): isErr = %v; expected %v", got, want)
+	}
+	ok, err, isErr = Err[Result[string, string, int]](42).Result()
+	if got, want := ok, ""; got != want {
+		t.Errorf("Result(): ok = %v; expected %v", got, want)
+	}
+	if got, want := err, 42; got != want {
+		t.Errorf("Result(): err = %v; expected %v", got, want)
+	}
+	if got, want := isErr, true; got != want {
+		t.Errorf("Result(): isErr = %v; expected %v", got, want)
+	}
 }
 
 func TestResultLayout(t *testing.T) {
@@ -70,24 +112,6 @@ func TestResultLayout(t *testing.T) {
 	}
 }
 
-func TestResultOKOrErr(t *testing.T) {
-	r1 := OK[Result[string, string, struct{}]]("hello")
-	if ok := r1.OK(); ok == nil {
-		t.Errorf("OK(): %v, expected non-nil OK", ok)
-	}
-	if err := r1.Err(); err != nil {
-		t.Errorf("Err(): %v, expected nil Err", err)
-	}
-
-	r2 := Err[Result[bool, struct{}, bool]](true)
-	if ok := r2.OK(); ok != nil {
-		t.Errorf("OK(): %v, expected nil OK", ok)
-	}
-	if err := r2.Err(); err == nil {
-		t.Errorf("Err(): %v, expected non-nil Err", err)
-	}
-}
-
 func TestAltResult1(t *testing.T) {
 	type alt1[Shape, OK, Err any] struct {
 		_     [0]OK