sliceutil: helpers for mid-slice insert/delete.

Manipulating the hand, deck, etc. is going to use these operations a lot.

cardsim/deck.go

@@ -31,8 +31,8 @@ func (d *Deck[C]) Len() int {
 	return len(d.cards)
 }
 
-// Insert puts a card at a specific location in the Deck. The card previously
-// at that location and all locations after are shifted one card later.
+// Insert puts one or more cards at a specific location in the Deck. Cards
+// at that location and all locations after are shifted deeper into the deck.
 // Negative indexes are counted from the bottom of the deck. BottomOfDeck is
 // a sentinel value for the bottommost position; -1 is one card above.
 //
@@ -44,7 +44,7 @@ func (d *Deck[C]) Len() int {
 // WarningTopClamped. Like all warnings, these can be safely ignored and the
 // program is in a well-defined state, but you may want to check for them
 // if you expect some other behavior.
-func (d *Deck[C]) Insert(idx int, card Card[C]) error {
+func (d *Deck[C]) Insert(idx int, card ...Card[C]) error {
 	var errs ErrorCollector
 	// Calculate actual target index.
 	switch {
@@ -60,14 +60,7 @@ func (d *Deck[C]) Insert(idx int, card Card[C]) error {
 		idx += d.Len()
 	}
 	// remaining case: 0 <= idx <= d.Len(), which is a normal forward insert index.
-
-	// Place new card on bottom and "bubble" into position.
-	// Takes O(N) time. If this turns out to be a problem, implement a more
-	// efficient data structure.
-	d.cards = append(d.cards, card)
-	for i := len(d.cards) - 1; i > idx; i-- {
-		d.cards[i], d.cards[i-1] = d.cards[i-1], d.cards[i]
-	}
+	d.cards = InsertInto(d.cards, idx, card...)
 	return errs.Emit()
 }