C Lambda Type Inference

One of the limitations of C# type inference is that you cannot use it to infer the type of a lambda expression. For example, the following code will not compile

var f = () => 4;

Normally this is not too much of an issue because you can just explicitly declare the type of the lambda expression.

Func<int> f = () => 4;

However, this can be annoying at times. Once you start defining complex lambda expressions the Func/Action declaration can be quite convoluted. Even worse, if your lambda returns an anonymous type, there is no way to declare a Func<> with the anonymous type parameter because you cannot describe it’s shape.

Func<'> f = () => new { Name = "foo" };

This is fixable though by using type inference. The method is very similar to other anonymous type type tricks. While lambda type inference is not supported for variable declaration it is supported for parameters. C# supports return type inference so that can be used to type the variable.

static Func<T> Lambda<T>(Func<T> del)
{
    return del;
}

static void Main(string[] args)
{
    var f = Lambda(() => new { Name = "foo" });
}