Question

I think my mind is exploding trying to figure out Funcs… If this makes no sense, I apologize, right now it make sense to me but its been a long day already ….

1) Assuming you are given a func which takes in T and outputs a string:

 Func<T, string> 

Can you transform that into a func that take in a T and returns a bool based on some logic (in this case if the returned string is empty (String.IsNullOrWhiteSpace)?

 Func<T, bool> 

2) Can you do the same thing if you are given an

Expression<Func<T, string>>

and need to convert it to a

Func<T, bool>

that returns true/false based on if the returned string is empty (String.IsNullOrWhiteSpace)?

Thanks

Answer 1

for the first part you can even make some "higher"-order function:

Func<A,C&gt MapFun<A,B,C&gt(Func<A,B&gt input, Func<B,C&gt transf)
{
   return a => transf(input(a));
}

use with

Func <T,string> test = ...
var result = MapFun(test, String.IsNullOrWhiteSpace);

(I hope C# type type inference is working here)

If you define this as extension on Func it gets even easier:

public static class FuncExtension
{
    public static Func<A,C> ComposeWith<A,B,C&gt(this Func<A,B> input, Func<B,C> f)
    {
         return a => f(input(a));
    }
}

here is a very simple test:

Func<int, string&gt test = i =&gt i.ToString();
var result = test.ComposeWith(string.IsNullOrEmpty);

For the second one: I think you can compile the expression into a "real" Func and then use the above code. see MSDN Docs on Expression.Compile

PS: renamed the function to better match it’s intend (it’s function composition)