4 ms·

To date, C's most proximate (management-friendly, technically similar, programmer-skill-adjacent) competition has been c++. (I'm trying to lay the groundwork fo

To date, C's most proximate (management-friendly, technically similar, programmer-skill-adjacent) competition has been c++. (I'm trying to lay the groundwork for the next statement: I'm not claiming this is good, and excited to see Rust and friends as serious contenders. Stay with me.) Even in c++20, there are things you can do with macros you can't do in the language. This may change when reflection lands in c++2x, but I won't be able to use it for years and widespread adoption won't be possible for another decade.

spaetzleesser 5y ago
When I look at a lot of things that are done with reflection in C# I personally would much prefer the preprocessor and macros. Things that could be done in a type safe manner with a macro in a few lines become way more complex when using reflection.
- mumblemumble 5y ago
  Could I beg of you to give an example? Back when I was working in C#, there were quite a few times when I'd encounter things being done with reflection that I wish had been done with less code and a more type safe manner by just... not using reflection. I always just assumed a lot of that was just bad habits left over from the .NET 1.0 days, back before generics. So I'm curious if there's much overlap there? If it's only a subset, I don't know C as well as I'd like, so it would be interesting to see something that the C preprocessor handles better.
  - spaetzleesser 5y ago
    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.
    - mumblemumble 5y ago
      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?
      - gsmecher 5y ago
        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/ https://digip.org/jansson/ [2]: https://www.gnu.org/software/libmicrohttpd https://www.gnu.org/software/libmicrohttpd
- touisteur 5y ago
  I'm a huge fan of java because of reflection. It can be so empowering and awesome. But lately I've come to prefer codegen+JIT when possible. So, discovery through introspection, and to call/read/modify stuff I'll generate the code.

spaetzleesser 5y ago

When I look at a lot of things that are done with reflection in C# I personally would much prefer the preprocessor and macros. Things that could be done in a type safe manner with a macro in a few lines become way more complex when using reflection.

mumblemumble 5y ago
Could I beg of you to give an example? Back when I was working in C#, there were quite a few times when I'd encounter things being done with reflection that I wish had been done with less code and a more type safe manner by just... not using reflection. I always just assumed a lot of that was just bad habits left over from the .NET 1.0 days, back before generics. So I'm curious if there's much overlap there? If it's only a subset, I don't know C as well as I'd like, so it would be interesting to see something that the C preprocessor handles better.
- spaetzleesser 5y ago
  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.
  - mumblemumble 5y ago
    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?
    - gsmecher 5y ago
      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/ https://digip.org/jansson/ [2]: https://www.gnu.org/software/libmicrohttpd https://www.gnu.org/software/libmicrohttpd
touisteur 5y ago
I'm a huge fan of java because of reflection. It can be so empowering and awesome. But lately I've come to prefer codegen+JIT when possible. So, discovery through introspection, and to call/read/modify stuff I'll generate the code.