Make Operation generic

From https://github.com/anacrolix/stm/commit/80e033aa1f2218b83fb5891671ed795de72e19d5

1 files changed, 11 insertions, 12 deletions

diff --git a/funcs.go b/funcs.go
index 3336c71..54576ea 100644
--- a/funcs.go
+++ b/funcs.go
@@ -39,7 +39,7 @@ func newTx() *Tx {
 	return tx
 }
 
-func WouldBlock(fn Operation) (block bool) {
+func WouldBlock[R any](fn Operation[R]) (block bool) {
 	tx := newTx()
 	tx.reset()
 	_, block = catchRetry(fn, tx)
@@ -51,7 +51,7 @@ func WouldBlock(fn Operation) (block bool) {
 }
 
 // Atomically executes the atomic function fn.
-func Atomically(op Operation) interface{} {
+func Atomically[R any](op Operation[R]) R {
 	expvars.Add("atomically", 1)
 	// run the transaction
 	tx := newTx()
@@ -116,20 +116,19 @@ func AtomicSet[T any](v *Var[T], val interface{}) {
 
 // Compose is a helper function that composes multiple transactions into a
 // single transaction.
-func Compose(fns ...Operation) Operation {
-	return func(tx *Tx) interface{} {
+func Compose[R any](fns ...Operation[R]) Operation[struct{}] {
+	return VoidOperation(func(tx *Tx) {
 		for _, f := range fns {
 			f(tx)
 		}
-		return nil
-	}
+	})
 }
 
 // Select runs the supplied functions in order. Execution stops when a
 // function succeeds without calling Retry. If no functions succeed, the
 // entire selection will be retried.
-func Select(fns ...Operation) Operation {
-	return func(tx *Tx) interface{} {
+func Select[R any](fns ...Operation[R]) Operation[R] {
+	return func(tx *Tx) R {
 		switch len(fns) {
 		case 0:
 			// empty Select blocks forever
@@ -154,12 +153,12 @@ func Select(fns ...Operation) Operation {
 	}
 }
 
-type Operation func(*Tx) interface{}
+type Operation[R any] func(*Tx) R
 
-func VoidOperation(f func(*Tx)) Operation {
-	return func(tx *Tx) interface{} {
+func VoidOperation(f func(*Tx)) Operation[struct{}] {
+	return func(tx *Tx) struct{} {
 		f(tx)
-		return nil
+		return struct{}{}
 	}
 }