返回语法有点奇怪[重复]

Posted 2021-04-14

这个问题在这里已有答案：

• What is recursion and when should I use it? 40个答案

经过几年的html / ASP，我回到了C＃编程。我遇到过这些问题并且找不到它的作用。这是一个类中的方法：

private string PeekNext()
{
    if (pos < 0)
        // pos < 0 indicates that there are no more tokens
        return null;
    if (pos < tokens.Length)
    {
        if (tokens[pos].Length == 0)
        {
            ++pos;
            return PeekNext();
        }
        return tokens[pos];
    }
    string line = reader.ReadLine();
    if (line == null)
    {
        // There is no more data to read
        pos = -1;
        return null;
    }
    // Split the line that was read on white space characters
    tokens = line.Split(null);
    pos = 0;
    return PeekNext();
}

是否会在其他一些返回发生之前调用自己？

这里发生了什么，从来没有看到一种方法回归自己！？返回什么，空字符串或什么......？或者也许我以前错过了它。

也许简单但令我困惑。

答案

private string PeekNext()
    {
        if (pos < 0)
            // pos < 0 indicates that there are no more tokens
            return null;
        if (pos < tokens.Length)
        {
            if (tokens[pos].Length == 0)
            {
                ++pos;
                return PeekNext();
            }
            return tokens[pos];
        }
        string line = reader.ReadLine();
        if (line == null)
        {
            // There is no more data to read
            pos = -1;
            return null;
        }
        // Split the line that was read on white space characters
        tokens = line.Split(null);
        pos = 0;
        return PeekNext();

另一答案

尽管该方法依赖于外部（类）变量，并且可能应该重构以将其依赖项作为参数，但非递归版本可能如下所示：

private string PeekNext()
{
    while (pos >= 0)
    {
        if (pos < tokens.Length)
        {
            if (tokens[pos].Length == 0)
            {
                ++pos;
                continue;
            }
            return tokens[pos];
        }
        string line = reader.ReadLine();
        if (line == null)
        {
            // There is no more data to read
            pos = -1;
            return null;
        }
        // Split the line that was read on white space characters
        tokens = line.Split(null);
        pos = 0;
    }
    // pos < 0 indicates that there are no more tokens
    return null;
}