Pointless .Net Feature of the Day

CPallini

At first glance, it looks they are coming back to the hatred C/C++ header/source file mechanism. :laugh:

OriginalGriff

It's for use in a partial class, so you could declare the partial method in the designer code for a WinForms app for example, and implement it in the user defined code for the same class. The difference is that the method can be called from the designer code because it will compile cleanly. This is still the case if the implementation of the partial method is never provided: the compiler will remove the partial method and the call to it if the concrete version is not written, and you still won't get a compiler error. Think of it as a sort-of optional private abstract method and you're about there.

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GKP1992

Where is YAGNI when you need it. Google trends[^] results sort of agree with your feelings, as do I.

RugbyLeague

It's mostly for generated code

den2k88

CPallini wrote:

they are coming back to the hatred rational, sensible, beloved C/C++ header/source file

FTFY

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Marc Clifton

The cool thing in the code below is that if you don't define LOGGING, not only does the partial method go away, but any calls to the method are also removed.

#define LOGGING

using System;

namespace PartialMethodTest
{
partial class Foo
{
partial void Log(string msg);

    public void DoSomething()
    {
        Log("Fizbin");
    }
}

#if LOGGING
partial class Foo
{
partial void Log(string msg)
{
Console.WriteLine(msg);
}
}
#endif

class Program
{
    static void Main(string\[\] args)
    {
        new Foo().DoSomething();
    }
}

}

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realJSOP

It's still pointless.

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CPallini

Quote:

but any calls to the method are also removed.

Wouldn't that be disastrous if the method is intended to produce side-effects?

den2k88

CPallini wrote:

if the method is intended to produce side-effects

If the programmer is a donkey, giving him/her a compiler is disastrous.

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CPallini

Unless you are haskelling yourself too much, most methods do have side effects.

Kornfeld Eliyahu Peter

I'm not sure such a code-remove by the compiler is 'cool'... While removing unused code while optimizing is good thing, removing unimplemented code just because it signed 'partial' definitely illogical... And to be honest - why would I define a private method and not implement it? It is definitely smells like a language feature added to support half-visual development with code generators... Outside of that context I see it very disturbing...

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RugbyLeague

I can't say I have ever found a use for it - although that might be because I didn't know it existed until your post :)

CPallini

Yes, code generators me think.

OriginalGriff

The people defining and the people using may be different people - this is only applicable to partial classes, remember - so there is a very good chance that the partial definition and its implementation are in different files, just as InitializeComponent is defined in the designer.cs file of a WinForms app, and called from the .cs file. I've not used it, but I can see advantages in a "team written" class, in that I write a "frame" which calls partial methods that are implemented by other team members in different files. As has been mentioned, it could be very useful for automated designers, allowing the user to define methods only when he needs them without having to mess around with delegates. Or tracing information only available in debug builds, which isn't even called in release giving slightly higher performance.

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Johnny J

Dunno. If I had a method whereby I could do just a part of my work, that would definitely be desired... :rolleyes:

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den2k88

"Side" effects are really something that need to be reduced. Methods should have only intended effects and possibly no side effect. If a method is to be implemented by the user of a class then it is part of the 'contract' to be respected when writing the user component - meaning it's up to the end user (programmer) to implement all the required effects and side effects.

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PIEBALDconsult

I agree.

CPallini

Intended-side-effects were intended :-D. That is side-effects in the functional meaning (in constrast with 'pure' functions, Haskell was the hint). Unintended side effects are just evil.

Mladen Jankovic

Judging by the restrictions imposed on partial methods: they cannot have return value (only void) or out parameters, they are intended to have side effects. Whether or not it is disastrous to skip side effect is another question. In original example (logging) it is not.

Sander Rossel

It was heavily used in Entity Framework DB First. I've used them a lot to extend generated classes with my own code. I've never used it for my own classes or outside of generated code.

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