該代碼片段是根據(jù)其前序和中序表示重建二叉樹。static public BinaryTreeNode<T> BuildFromPreAndInOrder<T>(ReadOnlySpan<T> preOrder, ReadOnlySpan<T> inOrder){    if (preOrder == null || preOrder.IsEmpty || inOrder == null || inOrder.IsEmpty) { return null; }    var val = preOrder[0];    BinaryTreeNode<T> root = new BinaryTreeNode<T>(val);    // this doesn't make sense    var splitPoint = MemoryExtensions.IndexOf<T>(inOrder, val);    if (splitPoint == -1) {        return null;    }    preOrder = preOrder.Slice(1);    var leftPart = inOrder.Slice(0, splitPoint);    var rightPart = inOrder.Slice(splitPoint + 1);    root.left = BuildFromPreAndInOrder(preOrder, leftPart);    root.right = BuildFromPreAndInOrder(preOrder, rightPart);    return root;}該節(jié)點(diǎn)很簡(jiǎn)單，所以我附上部分內(nèi)容。class BinaryTreeNode<T> : IEquatable<BinaryTreeNode<T>>{    public T key;    public BinaryTreeNode<T> left;    public BinaryTreeNode<T> right;}我嘗試在 .NET Core 3 Preview 7 SDK 上編譯它，但編譯器抱怨error CS1503: Argument 2: cannot convert from 'T' to 'System.ReadOnlySpan<T>'。為什么編譯器不能選擇正確的方法？檢查工具向我顯示了一個(gè)應(yīng)該能夠與此匹配的簽名。public static int IndexOf<T>([NullableAttribute(new[] { 0, 1 })] this ReadOnlySpan<T> span, [NullableAttribute(1)] T value) where T : IEquatable<T>;