在VS2012和VS2010上运行相同的程序表现出不同的行为

Question

I have .net 4.5 installed on my box and I understand that below behavior is related to difference in the way foreach captures closure between .net 3.5 and 4.

I'd like to better understand why running the same code in both VS 2012 and then with VS2010 shows different output when I compiling using .net Framework 4 in both cases, is it that VS 2012 runs csc with some special flag that cause it to capture closure?

var words = new[] { "foo", "bar", "baz", "beer" };
var actions = new List<Action>();
foreach (string word in words)
{
    actions.Add(() => Console.WriteLine(word));
}

actions.ForEach(e => e());

Output: With VS2010 and .net 4, above program yields "beer" 4 times

With VS2012 and .net 4:

foo bar baz beer

Answer 1

The fix for this was not part of .Net 4, it was part of C# 5. Thus, it is the compiler you are using, rather than the framework version you are targeting, that affects the behavior of this code.

This is discussed here , and officially declared here .

Answer 2

It was a kine of bug , that Microsoft fix it in VS2012. i don't know, did Microsoft fix it in VS 2010 in Last SP?. if you test it please inform us.