How to force Visual Studio (C#) to compile sources according to ECMA-334 standard?

Question

How to force Visual Studio (C#) to compile sources according to ECMA-334 standard?

For example the below code is not valid in ECMA-334 standard:

foreach (var item in custQuery)
{
    Console.WriteLine("Name={0}, Phone={1}", item.Name, item.Phone);
}

Because var is not a ECMA-334 standard keyword. I want to VS warns me in these situations.

Answer 1

You can use the "Language Version" option (aka langversion at the command line). It is on the build tab, under advanced options. You would select ISO-2 for this case.

Note that this is not a backwards compatibility mode. It merely bars you from using features that became available in versions newer than the specified version.

Eric Lippert has a detailed explanation of the use and purpose of the langversion option.

To note how it is not a full backwards compatibility mode, take this example from the article:

class C
{
    public static bool operator < (C c1, C c2) { return true; }
    public static bool operator > (C c1, C c2) { return true; }
    public static bool operator < (bool b1, C c2) { return true; }
    public static bool operator > (bool b1, C c2) { return true; }

    static C H = new C();
    static C I = new C();
    static C J = new C();
    static void G(bool b) { }
    static void Main()
    {
        G ( H < I > ( J ) );
    }
}

The setting langversion to C# 1.0 (ISO-1) bars this as a use of generics, but it was legal in that version of the compiler.