Method chaining with short-circuit parameter evaluation

[Richard Deeming]

If only there was some sort of site where people could write articles on exactly this issue[^]! ;P

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[Paul Conrad]

You could just toss a :thumbsup: in place of a 5 vote.

"I've seen more information on a frickin' sticky note!" - Dave Kreskowiak

[Septimus Hedgehog]

Have you looked at this CP article by Dimitri Nesteruk[^] It looks very useful.

"I do not have to forgive my enemies, I have had them all shot." — Ramón Maria Narváez (1800-68). "I don't need to shoot my enemies, I don't have any." - Me (2012).

[AspDotNetDev]

Yes! :thumbsup:

Thou mewling ill-breeding pignut!

[AspDotNetDev]

You were beat to the punch. :)

Thou mewling ill-breeding pignut!

[Gary Wheeler]

In C++ you could do this with an 'instance' call like this:

if (this != NULL)
{
return this->real_stuff;
}
else
{
return default_stuff;
}

As others have mentioned, in C# you can do this with extension methods:

namespace Test
{
public class Widget
{
}
public static class WidgetExtensions
{
static public void Method(this Widget _this)
{
if (_this != null)
{
Console.WriteLine("real widget");
}
else
{
Console.WriteLine("null widget");
}
}
}
class Program
{
static void Main(string[] args)
{
Widget widget = null;

        widget.Method();
        
        widget = new Widget();
        
        widget.Method();
    }
}

}

results in the output

null widget
real widget

Software Zen: delete this;

[Jorgen Andersson]

That settles it for me, I want voting back. :thumbsup:

People say nothing is impossible, but I do nothing every day.

[Jorgen Andersson]

System.DBNull is an example of the pattern. And I can't describe in words how much I dislike it.

People say nothing is impossible, but I do nothing every day.

[Septimus Hedgehog]

So I was. Great minds think alike but in my case I'll pass up on the citation. ;) Hopefully it'll convince Muppet Maunder to read it and see if helps him.

"I do not have to forgive my enemies, I have had them all shot." — Ramón Maria Narváez (1800-68). "I don't need to shoot my enemies, I don't have any." - Me (2012).

[Chris Maunder]

I am humbled and ashamed. And have just found an endless opportunity for way, way more procrastination.

cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP

[Chris Maunder]

I respect a man who prefers power drills and small explosives where others would wimp out and use tweezers. :thumbsup:

cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP

[Chris Maunder]

Else? There is no else. Just blindly plow on!

cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP

[Pete OHanlon]

When I get the chance, I may just have a go at it. Need some free time first.

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

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

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[CodeHawkz]

The first code block doesn't make any sense to me but this line

var result = Test.NotNull(myObject).NotNull(myObject.MyProperty).IsPositive(myObject.MyProperty.Id);

can be represented like this, can't you?

var result = (myObject == null ? false: myObject.MyProperty == null ? false : IsPositive(myObject.MyProperty.Id);

Just bouncing off an idea :) P.S. You can do it much simpler by using exceptions, I believe Cheers

[NormDroid]

Aye :thumbsup:

Software Kinetics - Dependable Software news

[englebart]

Would the C# ?? operator help you?
Would that do what you want? It definitely saves typing.
http://msdn.microsoft.com/en-us/library/ms173224.aspx

[Cesar de Souza]

Not really an answer for the question you asked, but just a comment about error handling. A good strategy to avoid endless nested checks in error handling is to handle the opposite case first. So instead of writing

Test.NotNull(myObject);
if (myObject != null)
{
Test.NotNull(myObject.MyProperty);
if (myObject.MyProperty != null)
Test.IsPositive(myObject.MyProperty.Id);
...
}

we would have

Test.NotNull(myObject);
if (myObject == null)
return;

Test.NotNull(myObject.MyProperty)
if (myObject.MyProperty == null)
return;

Test.IsPositive(myObject.MyProperty.Id);

...

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[Super Lloyd]

Chris Maunder wrote:

I was thinking it would be really cool to be able to do

Test.NotNull(myObject).NotNull(myObject.MyProperty).IsPositive(myObject.MyProperty.Id);

You can do that with extension methods! Just saying! ;)

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[Fabio Franco]

Chris Maunder wrote:

So this got me thinking: You can do

if (myObject != null && myObject.MyProperty != null)

because of short circuit boolean evaluation in C#, but I was wondering, with my fairly mainstream experience in languages, if there are languages out there that would allow chaining of methods with short circuit evaluation.

Well, I find myself doing a lot of those kind of checks and it would save me a lot of time and potential bugs if there was such a language. But now you have just stimulated me to think about a general purpose solution in C#. Maybe if I find something I'll post it on tips and tricks.

To alcohol! The cause of, and solution to, all of life's problems - Homer Simpson ---- Our heads are round so our thoughts can change direction - Francis Picabia

[Chris Maunder]

Not sure how that counts as handling the opposite case first, but I see what you mean and I do do that, though I do try and have only 2 exit points in a routine: 1 at the top when input fails, and the return at the end. Hence my thought that it would be nice having a single chained line at the top. All good discussion though. I love it.

cheers, Chris Maunder The Code Project | Co-founder Microsoft C++ MVP