[Mono-dev] gmcs and The Future

[Marek Safar]

Hi,
> On Thu, 2009-02-05 at 12:10 -0500, Avery Pennarun wrote:
>   
>> (The reason I use cpp, incidentally, is so I can implement C-style
>> assert() and check() macros that actually print the condition being
>> tested as part of the assertion message.  There seems to be no other
>> way to do this in C#, which is too bad.)
>>     
>
> There is now.  It's not the most performant technique around, but your
> Assert() or Check() methods could take an Expression<T>.  The
> Expression<T> can then be converted into a string for diagnostic
> messages, and converted into a delegate for the actual condition check,
> e.g.:
>
> 	[Conditional("DEBUG")]
> 	static void Assert<T>(T value, Expression<Func<T, bool>> e)
> 	{
> 		Func<T,bool> d = e.Compile();
> 		if (!d (value)) {
> 			// Convert `e' to a string and log
> 		}
> 	}
>
> 	// ...
>
> 	Assert(self, v => v != null);
>   

Here is slightly simplified version

    [Conditional("DEBUG")]
    static void Assert (Expression<Func<bool>> e)
    {
        var d = e.Compile ();
        if (!d ()) {
            Console.WriteLine (((LambdaExpression)e).Body.ToString ());
        }
    }

    public static void Main ()
    {
        object self = null;
        Assert (() => self != null);
    }


Marek