C# - LINQ First() 和隐式引用？

Question

我有一些代码，乍一看对我来说毫无意义。

问题：这里是否存在某种隐式引用？似乎只添加了不匹配的项目，'if' 的第一部分什么也没做。我说得对吗？（我已将我的评论 (///) 添加到我理解的内容中以解决我的问题）。 (//) 注释为原代码注释

 public static List<BAPresModel> MergeBudgetApprovalByProgramPMLists(
    List<BAPresModel> sourceList, List<BAPresModel> destList)
{
    /// we create this and use it but it seems to never impact destList that I can tell
    BAPresModel dstBA = new BAPresModel();

    // Merge sourceList into destList.
    foreach (BAPresModel sl in sourceList)
    {
        var qryDestList = from dl in destList
                          where sl.FiscalYearID == dl.FiscalYearID
                          where sl.X == dl.X
                          where sl.Y == dl.Y
                          select dl;
        if (qryDestList.Count() > 0)  // we found a match in the destination list.
        {
            /// I researched -First()- but don't see anything clarifying my question
            /// Is this creating a reference back to destList from dstBA somehow?
            dstBA = qryDestList.First();
            /// this applies the math (adding sl.X to dstBA.X )
            dstBA.X = Maths.AddNullableDecimals(dstBA.X, sl.X);
            dstBA.Y = Maths.AddNullableDecimals(dstBA.Y, sl.Y);
        }
        else  // no match, so add the sourceList item to the destination list.
        {
            destList.Add(sl);
        }
    }

    /// as far as I can tell the only thing this method actually does is return the original
    /// destList with 'sl' matched items added to it
    /// all of the work on dstBA is useless??
    return destList;
}

感谢您的宝贵时间和评价

Answer 1

假设 BPAPresModel 是 class

      dstBA = qryDestList.First();

有效地获取指向该查询返回的第一个匹配条目的指针。

        /// this applies the math (adding sl.X to dstBA.X )
        dstBA.X = Maths.AddNullableDecimals(dstBA.X, sl.X);
        dstBA.Y = Maths.AddNullableDecimals(dstBA.Y, sl.Y);

所以这两行在原来的 destList

中改变了它

Class 类型在 c# 中称为 'reference' 类型。因为在

这样的事情中

   BAPresModel foo = SomeFunction();

foo 是对堆上实际对象的引用。如果您是 C 或 C++ 开发人员，请思考

   BAPresModel *foo = SomeFunction();

所以不是 'implicit' 参考，而是 'actual' 参考

C# - LINQ First() 和隐式引用？

C# - LINQ First() and an implicit reference?

c#

linq