feat: Add BatchN to create a batch with an initial capacity.

batch.go

@@ -72,6 +72,13 @@ func (b *Batch) Queue(query string, arguments ...any) *QueuedQuery {
 	return qq
 }
 
+// BatchN returns a new Batch with an initial capacity of n.
+// This is useful to avoid allocations if you know beforehand how many queries
+// at least you want to enqueue.
+func BatchN(n int) Batch {
+	return Batch{queuedQueries: make([]*QueuedQuery, 0, n)}
+}
+
 // Len returns number of queries that have been queued so far.
 func (b *Batch) Len() int {
 	return len(b.queuedQueries)

batch_test.go

@@ -31,7 +31,7 @@ func TestConnSendBatch(t *testing.T) {
 	);`
 		mustExec(t, conn, sql)
 
-		batch := &pgx.Batch{}
+		batch := pgx.BatchN(7)
 		batch.Queue("insert into ledger(description, amount) values($1, $2)", "q1", 1)
 		batch.Queue("insert into ledger(description, amount) values($1, $2)", "q2", 2)
 		batch.Queue("insert into ledger(description, amount) values($1, $2)", "q3", 3)
@@ -40,7 +40,7 @@ func TestConnSendBatch(t *testing.T) {
 		batch.Queue("select * from ledger where false")
 		batch.Queue("select sum(amount) from ledger")
 
-		br := conn.SendBatch(ctx, batch)
+		br := conn.SendBatch(ctx, &batch)
 
 		ct, err := br.Exec()
 		if err != nil {