Method chaining with short-circuit parameter evaluation

[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]

You were beat to the punch. :)

Thou mewling ill-breeding pignut!

[AspDotNetDev]

Yes! :thumbsup:

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

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

[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

[Alan Balkany]

It might be simpler to just push the test down into a function call. This keeps the calling method simple, making the code more understandable and maintainable. Anyone maintaining the code doesn't have to reason about a unique control structure, and can skip all the details to focus on the overall algorithm. If they're curious about the test, they can optionally browse the testing function. The chaining looks cool, but is more complex than a sequence of plain, vanilla, if statements.

[Cesar de Souza]

Sorry, I should have meant "handle the error case first and exit as soon as possible", even if this "as soon as possible" will only occur in the middle of the function. Usually I don't have problems with multiple exit points in a function. Those are particularly useful, for example, when implementing a syntax parser from a LL(1) grammar. Another situation may happen, for example, if you are in the middle of a very nested loop and would like to exit them all. Refactoring the loop into its own function and using a return is often one of the clearest ways to quit all loops at once, specially in comparison with the alternative which is to maintain quite a number of done variables guarding the loop exits as in

for (int i = 0; i < n && !done; i++)

By the way, another sensible alternative for this case is also to use a goto statement, this being one of the few justified cases for using it. I know this doesn't have anything to do with your question either, but I am just keeping up the discussion :)

Interested in Machine Learning in .NET? Check the Accord.NET Framework. See also Haar-feature Object Detection (With The Viola-Jones Framework) in C#