C# inline lambda expression

Question

the title is a mouthful and not even sure it's accurate (couldn't make much sense of this), so I'll try to explain what I'd like to accomplish in C# by using equivalent javascript. Any suggestion as to what I should title this question is very much welcome.
In C#, say I have defined this function:

Func<string, string> getKey = entity => {
    switch(entity) {
        case "a":
            return "foo";
        case "b":
            return "bar";
        default:
            return "baz";
    }
};

string key = getKey(/* "a", "b", or something else */);

Now suppose I don't want to define the getKey function explicitly, but use it anonymously as I would in this equivalent javascript snippet:

string key = (function(entity) {
    switch(entity) {
        case "a":
            return "foo";
        case "b":
            return "bar";
        default:
            return "baz";
    }
}(/* "a", "b", or something else */));

How would I go about writing that in C#? I tried:

string key = (entity => {
    switch(entity) {
        case "a":
            return "foo";
        case "b":
            return "bar";
        default:
            return "baz";
    }
})(/* "a", "b", or something else */);

but I get syntax error CS0149: Method name expected.
Thanks in advance, cheers.

You can name it C# inline lambda expression – DDan Apr 08 '16 at 09:36 — DDan, Apr 08 '16 at 09:36

score 6 · Accepted Answer · edited Apr 08 '16 at 09:42

6

IMO, the nearest equivalent is this:

var key = new Func<string, string>(entity =>
{
    switch (entity)
    {
        case "a":
            return "foo";
        case "b":
            return "bar";
        default:
            return "baz";
    }
})("a");

edited Apr 08 '16 at 09:42

iggymoran

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answered Apr 08 '16 at 09:35

Dennis

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@iggymoran I was just about to write the same thing; I tried it first with `("a")` and it worked like a charm, so thanks @Dennis! – Andrea Aloi Apr 08 '16 at 09:49

Peter Ferak · Answer 2 · 2016-04-08T11:50:36.577

C# is a compiled language and thus different from javascript in a number of ways. What you are looking for is a closure https://en.wikipedia.org/wiki/Closure_(computer_programming). And those are possible in C# (for example Linq).

But I think that what you are looking for can be solved nicely with extension methods (https://msdn.microsoft.com/en-us//library/bb383977.aspx):

using ExtensionMethods;
using System;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("a".ConvertKey());
        }
    }
}

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static string ConvertKey(this String key)
        {
            switch (key)
            {
                case "a":
                    return "foo";
                case "b":
                    return "bar";
                default:
                    return "baz";
            }
        }
    }
}

EDIT: Same program using Linq:

using System;
using System.Linq;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(new[] { "a" }.Select(entity =>
            {
                switch (entity)
                {
                    case "a":
                        return "foo";
                    case "b":
                        return "bar";
                    default:
                        return "baz";
                }
            }).First());
            Console.ReadKey();
        }
    }
}

You can think of "Select" as "map" in functional terms. Hope this helps!

I *knew* it had something to do with closures, cause that's what the equivalent `javascript` code is all about, too. I just chickened out in using the term :) — Andrea Aloi, Apr 08 '16 at 09:53
About your answer: neat, but way too cumbersome, my whole idea was to *save* code since I only need the closure in that one place; otherwise an extension method would have been my choice as well. — Andrea Aloi, Apr 08 '16 at 09:56
Alright. You could use Linq to write closures over lists (but they don't work on single values, as you'll see in the example I had to instantiate an array with a single value). Previous program with Linq: — Peter Ferak, Apr 08 '16 at 11:30

C# inline lambda expression

2 Answers2