workaround for go generics

Author: MarcoPolo

util.go

@@ -125,5 +125,5 @@ func ForEach(m Multiaddr, cb func(c Component) bool) {
 
 func (m Multiaddr) Match(p ...meg.Pattern) (bool, error) {
 	matcher := meg.PatternToMatcher(p...)
-	return meg.Match(matcher, m)
+	return meg.Match(matcher, m, func(c *Component) meg.Matchable { return c })
 }

x/meg/bench_test.go

@@ -29,8 +29,12 @@ func preallocateCapture() *preallocatedCapture {
 
 var webrtcMatchPrealloc *preallocatedCapture
 
+func componentPtrToMatchable(c *multiaddr.Component) *multiaddr.Component {
+	return c
+}
+
 func (p *preallocatedCapture) IsWebRTCDirectMultiaddr(addr multiaddr.Multiaddr) (bool, int) {
-	found, _ := meg.Match(p.matcher, addr)
+	found, _ := meg.Match(p.matcher, addr, componentPtrToMatchable)
 	return found, len(p.certHashes)
 }
 
@@ -107,7 +111,7 @@ func isWebTransportMultiaddrPrealloc() *preallocatedCapture {
 
 func IsWebTransportMultiaddrPrealloc(m multiaddr.Multiaddr) (bool, int) {
 	p := isWebTransportMultiaddrPrealloc()
-	found, _ := meg.Match(p.matcher, m)
+	found, _ := meg.Match(p.matcher, m, componentPtrToMatchable)
 	return found, len(p.certHashes)
 }
 
@@ -365,7 +369,7 @@ func BenchmarkIsWebTransportMultiaddrNoCapturePrealloc(b *testing.B) {
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		isWT, _ := meg.Match(wtPreallocNoCapture, addr)
+		isWT, _ := meg.Match(wtPreallocNoCapture, addr, componentPtrToMatchable)
 		if !isWT {
 			b.Fatal("unexpected result")
 		}

x/meg/meg.go

@@ -69,7 +69,10 @@ type Matchable interface {
 // Match returns whether the given Components match the Pattern defined in MatchState.
 // Errors are used to communicate capture errors.
 // If the error is non-nil the returned bool will be false.
-func Match[S ~[]T, T Matchable](matcher Matcher, components S) (bool, error) {
+// The ptrToMatchable function is used to convert type *T to a Matchable..
+// This is due to a limitation of Go generics, where we cannot say *T implements Matchable.
+// When meg moves out of the x/ directory, we can reference the `*Component` type directly and avoid this limitation.
+func Match[S ~[]T, T any, G Matchable](matcher Matcher, components S, ptrToMatchable func(*T) G) (bool, error) {
 	states := matcher.states
 	startStateIdx := matcher.startIdx
 
@@ -92,19 +95,20 @@ func Match[S ~[]T, T Matchable](matcher Matcher, components S) (bool, error) {
 
 	currentStates = appendState(currentStates, states, startStateIdx, nil, visitedBitSet)
 
-	for _, c := range components {
+	for ic := range components {
 		clear(visitedBitSet)
 		if len(currentStates.states) == 0 {
 			return false, nil
 		}
 		for i, stateIndex := range currentStates.states {
 			s := states[stateIndex]
-			if s.codeOrKind == matchAny || (s.codeOrKind >= 0 && s.codeOrKind == c.Code()) {
+			cPtr := ptrToMatchable(&components[ic])
+			if s.codeOrKind == matchAny || (s.codeOrKind >= 0 && s.codeOrKind == cPtr.Code()) {
 				cm := currentStates.captures[i]
 				if s.capture != nil {
 					next := &capture{
 						f: s.capture,
-						v: c,
+						v: cPtr,
 					}
 					if cm == nil {
 						cm = next

x/meg/meg_test.go

@@ -13,26 +13,30 @@ type codeAndValue struct {
 }
 
 // Code implements Matchable.
-func (c codeAndValue) Code() int {
+func (c *codeAndValue) Code() int {
 	return c.code
 }
 
 // Value implements Matchable.
-func (c codeAndValue) Value() string {
+func (c *codeAndValue) Value() string {
 	return c.val
 }
 
 // Bytes implements Matchable.
-func (c codeAndValue) Bytes() []byte {
+func (c *codeAndValue) Bytes() []byte {
 	return []byte(c.val)
 }
 
 // RawValue implements Matchable.
-func (c codeAndValue) RawValue() []byte {
+func (c *codeAndValue) RawValue() []byte {
 	return []byte(c.val)
 }
 
-var _ Matchable = codeAndValue{}
+var _ Matchable = &codeAndValue{}
+
+func codeAndValuePtrToMatchable(c *codeAndValue) *codeAndValue {
+	return c
+}
 
 func TestSimple(t *testing.T) {
 	type testCase struct {
@@ -106,12 +110,12 @@ func TestSimple(t *testing.T) {
 
 	for i, tc := range testCases {
 		for _, m := range tc.shouldMatch {
-			if matches, err := Match(tc.pattern, codesToCodeAndValue(m)); !matches {
+			if matches, err := Match(tc.pattern, codesToCodeAndValue(m), codeAndValuePtrToMatchable); !matches {
 				t.Fatalf("failed to match %v with %v. idx=%d. err=%v", m, tc.pattern, i, err)
 			}
 		}
 		for _, m := range tc.shouldNotMatch {
-			if matches, _ := Match(tc.pattern, codesToCodeAndValue(m)); matches {
+			if matches, _ := Match(tc.pattern, codesToCodeAndValue(m), codeAndValuePtrToMatchable); matches {
 				t.Fatalf("failed to not match %v with %v. idx=%d", m, tc.pattern, i)
 			}
 		}
@@ -125,7 +129,7 @@ func TestSimple(t *testing.T) {
 					return true
 				}
 			}
-			matches, _ := Match(tc.pattern, codesToCodeAndValue(notMatch))
+			matches, _ := Match(tc.pattern, codesToCodeAndValue(notMatch), codeAndValuePtrToMatchable)
 			return !matches
 		}, &quick.Config{}); err != nil {
 			t.Fatal(err)
@@ -172,7 +176,7 @@ func TestCapture(t *testing.T) {
 	_ = testCases
 	for _, tc := range testCases {
 		state, assert := tc.setup()
-		if matches, _ := Match(state, tc.parts); !matches {
+		if matches, _ := Match(state, tc.parts, codeAndValuePtrToMatchable); !matches {
 			t.Fatalf("failed to match %v with %v", tc.parts, state)
 		}
 		assert()
@@ -255,7 +259,7 @@ func FuzzMatchesRegexpBehavior(f *testing.F) {
 			return
 		}
 		p := PatternToMatcher(pattern...)
-		otherMatched, _ := Match(p, bytesToCodeAndValue(corpus))
+		otherMatched, _ := Match(p, bytesToCodeAndValue(corpus), codeAndValuePtrToMatchable)
 		if otherMatched != matched {
 			t.Log("regexp", string(regexpPattern))
 			t.Log("corpus", string(corpus))