Storing a Lambda Expression in a Variable

Question

I think my brain has become fried as i'm struggling to do something simple. In my application i have the following code to configure Nhibernate (my issue is not specific to Nhibernate).

return Fluently.Configure()
    .ExposeConfiguration(c => {
        c.EventListeners.PostInsertEventListeners = new IPostInsertEventListener[] { new LoggingEventListener() };
        c.EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[] { new LoggingEventListener() };
   });

However I need to store the configuration (the stuff inside ExposeConfiguration) inside a private variable. I can do the following:

return Fluently.Configure()
    .ExposeConfiguration(c => _configuration = c);

Where _configuration is a private variable. But this doesn't add my extra configuration options (the EventListeners stuff). I've played around with various things but i guess my lambda knowledge isn't as good as i thought.

I'd appreciate your help. Thanks

I think you should also post the declaration (delegate) of ExposeConfiguration, + what is it that you want to save in _configuration (declaration would also help). — Manish Basantani, Dec 07 '10 at 16:51

Colin Mackay · Accepted Answer · 2014-01-29T14:30:45.643

92

A lambda expression is just a delegate that often maps to one of the Func<T1, T2, ..., TResult> variants.

Func<T1, TResult> myVar = c => _configuration = c;

Replacing TResult and T1 with the relevant types.

That might work for you.

edited Jan 29 '14 at 14:30

answered Dec 07 '10 at 16:37

Colin Mackay

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1

+1, but note a lambda expression can map to any compatible delegate type. It's just often used with `Func<>` – JaredPar Dec 07 '10 at 16:39
1

Is it not the other way around? Func rather than Func, ... etc.? – NeverStopLearning Jan 29 '14 at 09:17
1

@NeverStopLearning Yes, you're right. I got the type parameters the wrong way around. I've corrected my answer. – Colin Mackay Jan 29 '14 at 14:31
Why am I getting a `cannot convert from 'System.Func' to 'System.Linq.Expressions>'`? Maybe it's one of the exceptions where it doesn't map - I'm trying to set a binding in Xamarin.Forms. – jbyrd Apr 07 '16 at 18:47
3

Great answer, although I was a little confused at first how T1 and TResult correspond with the function. Here's an example that may be a bit clearer: `Func numberToString = (num) => { return num + "";};` – frodo2975 Jul 19 '16 at 21:35

Alexandre Daubricourt · Answer 2 · 2021-07-09T08:16:28.583

1

With C# 7.0 local functions

TResult matchDuplicates (T1 c) => _configuration = c;

edited Jul 09 '21 at 08:16

answered Nov 16 '20 at 12:22

Alexandre Daubricourt

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score 0 · Answer 3 · edited Jun 15 '15 at 01:26

Sure. Assuming _configuration is going to store what you were using in your first bit of code. It should look something like this:

return Fluently.Configure().ExposeConfiguration(c => {
c.EventListeners.PostInsertEventListeners = _configuration;
c.EventListeners.PostUpdateEventListeners = _configuration;});

If there are any kind of cast errors from the compiler, you can always use:

_configuration.Cast<IPostInsertEventListeners>();

Storing a Lambda Expression in a Variable

3 Answers3

With C# 7.0 local functions

Linked