说我有以下的code（上下文范围缩小到保持的问题包括但不限于）

Say I have the following code (context narrowed down as to keep the question scope limited)

public static IEnumerable<Color> GetThemColors(){
	var ids = GetThePrimaryIds();
	foreach (int id in ids){
		yield return GetColorById(id);
	}
	ids = GetTheOtherIds();
	foreach (int id in ids){
		yield return GetOtherColorsById(id);
	}
}

我想将它们改写为这样的事情（这当然不编译

I would like to rewrite them to something like this (which off course doesn't compile

public static IEnumerable<Color> GetThemColors(){
	GetThePrimaryIds().Select(id=>yield return GetColorById(id));
	GetTheOtherIds().Select(id=>yield return GetOtherColorsById(id));		
}

关键的一点是，在我的第一个片段，我有两个的foreach枚举屈服，我不知道该怎么办的LINQ没有失去我的懒加载功能。

The key point being that in my first snippet I have two foreach enumerators yielding, which I don't know how to do in linq without loosing my lazy-loading features.

推荐答案

您想要 Concat的：

return GetThePrimaryIds().Select(id => GetColorById(id)).Concat(
    GetTheOtherIds().Select(id => GetOtherColorsById(id)));

另外请注意，你并不需要在lambda表达式收益率回报。