Macros on Steroids: How pure C can benefit from metaprogramming

Re:Macros on Steroids: How pure C can benefit from metaprogr... by spaetzleesser on Thursday July 22, 2021 @10:08PM (#27926477)

For example INotifyPropertyChanged which is used in WPF.

The typical implementation is something like this:

     public string CustomerName  
        {  
            get  
            {  
                return this.customerNameValue;  
            }  

            set  
            {  
                if (value != this.customerNameValue)  
                {  
                    this.customerNameValue = value;  
                    NotifyPropertyChanged();  
                }  
            }  
        }

When you have 20 properties you have a ton of repetitive code. With a preprocessor I could reduce each property to a one liner. You can also do tricks with reflection but that's way more complex to implement.

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Re:Macros on Steroids: How pure C can benefit from metaprogr... by mumblemumble on Friday July 23, 2021 @09:13AM (#27930264)

Yeah, there is that, but I wash hoping to see a great use case for C preprocessor macros. WPF data binding doesn't seem like good candidate for something you're likely to want to do in a C program.

Or were you really just meaning to advocate for metaprogramming in general?

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Re:Macros on Steroids: How pure C can benefit from metaprogr... by gsmecher on Friday July 23, 2021 @01:26PM (#27933312)

I design instrumentation for telescopes, in which C code on an embedded processor peeks and pokes device registers on an nearby FPGA. This C code forms an interface between hardware and the network.

In this system, I write a given function in C and surround it with a macro wrapper. This wrapper generates a JSON-RPC equivalent of the C function using the Jansson JSON library [1], complete with argument typechecking and error management. My C code can call the function normally, and an embedded webserver [2] can export it across the network where it's used fairly transparently by a Python stack on a control PC.

All three of these "embedded software" elements (the embedded webserver, the JSON library, and the FPGA interface) are very well suited to C. I have recently dabbled in moving parts of it to C++, and have found a few surprising impedance mismatches. (As I mentioned above, C++ still lacks reflection.)

The macros, here, are not for "elegance" or any other abstract purpose. They have allowed a ~80% reduction in boilerplate and an equally impressive reduction in the bugs and hassles associated with this kind of low-density, high-sprawl code.

[1]: https://digip.org/jansson/

[2]: https://www.gnu.org/software/libmicrohttpd

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