c# - 什么是 C++ 中拼接的 C# 替代方案

Question

我有一个 C++ 代码并尝试用 C# 编写

我想不出在 C# 中拼接的最佳替代方案

C++ 也有一个“查找”可以在 map 上工作，我想在字典上用 C# 实现它

Answer 1

在您的 C++ 示例中，您显示:

statement_tokens.splice(statement_tokens.begin(), tokens, tokens.begin(), next_sc);

根据我的理解(documentation)，这个重载需要一个插入位置、一个列表(相同类型)以及一个范围的第一个(包括)和最后一个(不包括)索引以拼接到插入位置, 然后将此范围插入到原始列表中。

更新:并且它从另一个列表中删除项目。我刚刚添加了该功能。

如果这是正确的，那么下面的扩展方法应该可以工作:

列表扩展方法 (检查此答案的末尾以了解此方法的其他重载)

public static class ListExtensions
{
    public static void Splice<T>(this List<T> list, int insertAtIndex, List<T> items, 
        int first, int last)
    {
        if (items == null) return;
        insertAtIndex = Math.Min(list.Count, Math.Max(0, insertAtIndex));
        first = Math.Min(items.Count - 1, Math.Max(0, first));
        last = Math.Min(items.Count, Math.Max(1, last));
        if (first >= last) return;

        list.InsertRange(insertAtIndex, items.GetRange(first, last - first));            
        items.RemoveRange(first, last - first);
    }
}

更新 2:现在，您似乎缺少 std::find_if 的另一个扩展方法，它返回指定范围内列表项的索引，基于如果项目满足某些条件则返回 true 的方法。因此，让我们将以下方法添加到上面的 ListExtensions 类中:

public static int FindIf<T>(this List<T> list, int start, int end, Func<T, bool> method)
{
    if (method == null) return end;
    if (!list.Any(method)) return end;
    start = Math.Min(list.Count - 1, Math.Max(0, start));
    end = Math.Min(list.Count, Math.Max(1, end));
    if (start >= end) return end;
    var range = list.GetRange(start, end - start);
    var index = range.IndexOf(list.First(method));
    if (index < start) return end;
    return index;
}

请注意，此方法的一个参数是一个函数，该函数采用 T 类型的项目并返回 bool。这将是一个简单的方法，用于检查我们的 token 的字符串值是否为分号:

static bool TokenIsSemicolon(EvlToken token)
{
    return (token != null && token.Str == ";");
}

现在，您可能会注意到我引用了 token.Str。这来自 EvlToken 类，创建该类是为了模仿 C++ 结构:

class EvlToken
{
    public enum TokenType { Name, Number, Single }
    public TokenType Type { get; set; }
    public string Str { get; set; }
    public int LineNo { get; set; }
}

现在我们可以完成对原始方法的转换，调用我们的FindIf 和Splice 扩展方法:

static bool MoveTokensToStatement(List<EvlToken> statementTokens, List<EvlToken> tokens)
{
    if (statementTokens == null || statementTokens.Count > 0) return false;
    if (tokens == null || tokens.Count == 0) return false;

    int nextSemiColon = tokens.FindIf(0, tokens.Count, TokenIsSemicolon);

    if (nextSemiColon == tokens.Count)
    {
        Console.WriteLine("Looked for ';' but reached the end of the file.");
        return false;
    }

    ++nextSemiColon;
    statementTokens.Splice(0, tokens, 0, nextSemiColon);
    return true;
}

额外的重载

为了完整起见，这里是扩展类以及文档中提到的其他两个重载:

public static class ListExtensions
{
    /// <summary>
    /// Transfers all elements from 'items' into 'this' at the specified index
    /// </summary>
    /// <typeparam name="T">The type of items in the list</typeparam>
    /// <param name="list">'this' instance</param>
    /// <param name="insertAtIndex">The index to insert the items</param>
    /// <param name="items">The list to transfer the items from</param>
    public static void Splice<T>(this List<T> list, int insertAtIndex,
        List<T> items)
    {
        if (items == null) return;
        list.Splice(insertAtIndex, items, 0, items.Count);
    }

    /// <summary>
    /// Transfers the element at 'itemIndex' from 'items' 
    /// into 'this' at the specified index
    /// </summary>
    /// <typeparam name="T">The type of items in the list</typeparam>
    /// <param name="list">'this' instance</param>
    /// <param name="insertAtIndex">The index to insert the item</param>
    /// <param name="items">The list to transfer the item from</param>
    /// <param name="itemIndex">The index of the item to transfer</param>
    public static void Splice<T>(this List<T> list, int insertAtIndex,
        List<T> items, int itemIndex)
    {
        list.Splice(insertAtIndex, items, itemIndex, itemIndex + 1);
    }

    /// <summary>
    /// Transfers the specified range of elements from 'items' 
    /// into 'this' at the specified index
    /// </summary>
    /// <typeparam name="T">The type of items in the list</typeparam>
    /// <param name="list">'this' instance</param>
    /// <param name="insertAtIndex">The index to insert the item</param>
    /// <param name="items">The list to transfer the item from</param>
    /// <param name="first">The index of the first item in the range</param>
    /// <param name="last">The exclusive index of the last item in the range</param>
    public static void Splice<T>(this List<T> list, int insertAtIndex, List<T> items, 
        int first, int last)
    {
        if (items == null) return;
        insertAtIndex = Math.Min(list.Count, Math.Max(0, insertAtIndex));
        first = Math.Min(items.Count - 1, Math.Max(0, first));
        last = Math.Min(items.Count, Math.Max(1, last));
        if (first >= last) return;

        list.InsertRange(insertAtIndex, items.GetRange(first, last - first));            
        items.RemoveRange(first, last - first);
    }

    /// <summary>
    /// Searches for the first item in the specified range that "method" returns true for
    /// </summary>
    /// <typeparam name="T">The type of items in the list</typeparam>
    /// <param name="list">'this' instance</param>
    /// <param name="start">The index of the first item in the range</param>
    /// <param name="end">The exclusive index of the last item in the range</param>
    /// <param name="method">A method which takes type 'T' and returns a bool</param>
    /// <returns>The index of the item, if found, otherwise 'end'</returns>
    public static int FindIf<T>(this List<T> list, int start, int end, Func<T, bool> method)
    {
        if (method == null) return end;
        if (!list.Any(method)) return end;
        start = Math.Min(list.Count - 1, Math.Max(0, start));
        end = Math.Min(list.Count, Math.Max(1, end));
        if (start >= end) return end;
        var range = list.GetRange(start, end - start);
        var index = range.IndexOf(list.First(method));
        if (index < start) return end;
        return index;
    }
}

示例用法

这是一个使用 EvlTokens 列表，然后调用 MoveTokensToStatement 两次的示例:

private static void Main()
{
    var tokens = new List<EvlToken>
    {
        new EvlToken {LineNo = 3, Str = "int", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 3, Str = "x", Type = EvlToken.TokenType.Name},
        new EvlToken {LineNo = 3, Str = "=", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 3, Str = "1", Type = EvlToken.TokenType.Number},
        new EvlToken {LineNo = 3, Str = "+", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 3, Str = "5", Type = EvlToken.TokenType.Number},
        new EvlToken {LineNo = 3, Str = ";", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = "Console", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = ".", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = "WriteLine", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = "(", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = "Hello World", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = ")", Type = EvlToken.TokenType.Single},
        new EvlToken {LineNo = 4, Str = ";", Type = EvlToken.TokenType.Single}
    };

    var statementTokens = new List<EvlToken>();

    MoveTokensToStatement(statementTokens, tokens);

    Console.WriteLine("Here is the result of calling 'MoveTokensToStatement' the first time:");
    Console.WriteLine(string.Join(" ", statementTokens.Select(t => t.Str)));
    statementTokens.Clear();

    MoveTokensToStatement(statementTokens, tokens);

    Console.WriteLine("\nHere is the result of calling 'MoveTokensToStatement' the second time:");
    Console.WriteLine(string.Join("", statementTokens.Select(t => t.Str)));
    statementTokens.Clear();


    Console.WriteLine("\nDone!\nPress any key to exit...");
    Console.ReadKey();
}

输出