Method chaining with short-circuit parameter evaluation

[Dalek Dave]

Do Not Procrastinate Today! Wait until tomorrow and have a whole day of it. Until then, stare at this picture[^] of a cat.

--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]

[peterchen]

Chris Maunder wrote:

I was drunk.

You always say that :cool:

ORDER BY what user wants

[Ennis Ray Lynch Jr]

The null object pattern.

public class Customer{}
public class NullCustomer : Customer{}

Then instead of assigning a customer reference to null you assign it to the null customer, etc. Then you can do all of your work without null checks. There are some instances where this works really, really, well. However, if you are chaining functions it is probably some sort of workflow so there maybe another solution that issue.

Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost "All users always want Excel" --Ennis Lynch

[Dalek Dave]

He's always drunk.

--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]

[Nagy Vilmos]

No. I always say that.

---

Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett

[Corporal Agarn]

I think you should ban him! :laugh: ;P

[Dalek Dave]

You're always drunk!

--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]

[Nagy Vilmos]

I may well be tonight.

---

Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett

[Shelby Robertson]

Norm .net wrote:

If voting was available, I would of shot you a 5, but alas.....

Seconded.

CPallini wrote:

You cannot argue with agile people so just take the extreme approach and shoot him. :Smile:

[Pete OHanlon]

There is a way that you could do this, but it would be much more trouble than it was worth, and it would definitely open up a whole world of hurt. Effectively, what would need to be implemented is an IL rewriter to manage and rewrite the chain internally. Then you could create a fluid interface that would need to be recognised as the item that needs rewriting.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

[Lost User]

Or a decorator, preferably combined with the NullObject-pattern :)

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] They hate us for our freedom![^]

[R Giskard Reventlov]

Not very elegant, even if you could. Nice to get all clever (over engineering is, surely, an anti-pattern) with code but sometime in the future some poor sap will have to maintain what you have put together so keep it simple and verbose.

"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." Red Adair. nils illegitimus carborundum me, me, me

[Ranjan D]

Yes my vote for extension methods :)

Ranjan.D

[Roger Wright]

I've heard of chaining programs and subprograms - using hpl on the HP 9825, for instance - but short circuit evaluation was never considered. Having never optimized a program for multi-processor environments, I have no idea how to do this, but you could launch a separate process for each of your levels of test, then cancel all if any one of them fails. It might not be useful, but it would certainly give the grunts whose job it is to debug things something interesting to do. :rolleyes:

Will Rogers never met me.

[Jibesh]

so who is really drunk here. was it me?

Jibesh V P

[Nemanja Trifunovic]

Out of curiosity, what would you do in the else section of such a call?

utf8-cpp

[AspDotNetDev]

There are a few ways you could do this, but one thing I've been meaning to write a tip/trick on (as soon as I figure out how it can be done) is the expression tree approach. You'd do this:

var result = SafeChain(A.b.c.d.e.f.g.h.i.j.k);

The parameter would be passed as an expression tree, which would then be evaluated in steps, making sure to check for nulls along the way. The first null would cause null to be returned, otherwise the result value would be returned. I imagine you could use the same approach with your method chaining / expression trees.

Thou mewling ill-breeding pignut!

[szukuro]

In C# you can implement this k<ind of chaining using extension methods and expressions trees. The extension method (somewhat combined version of the two above):

    public static U NotNull(this T myObject, Expression expression) 
        where U : class
    {
        if (myObject == null)
            return null;
        else
        {
           var func = expression.Compile();
            return func();
        }
    }

Usage (returns either null if there's a null in the chain, or the value of MySubProperty, with almost the same syntax as above):

var value = myObject.NotNull(() => myObject.MyProperty).NotNull(() => myProperty.MySubProperty);

The only downside I found that in this case you have to declare a variable of type MyProperty for use in the second lambda expression. Maybe there's a way around it, but I didn't manage to find one as of yet. That can be changed though if the input remains myObject and the expression consists of the full path i. e. () => myObject.MyProperty.MySubProperty.

[OriginalGriff]

Chris Maunder wrote:

Am I procrastinating?

Yep! But then, you probably don't want to fix RootAdmin - it's down according to http://www.downforeveryoneorjustme.com/rootadmin.com[^]

If you get an email telling you that you can catch Swine Flu from tinned pork then just delete it. It's Spam.

[szukuro]

Actually to be passed as an expresion tree you'd have to write:

var result = SafeChain(**() =>**A.b.c.d.e.f.g.h.i.j.k);

But I agree that this is the way to do it.