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60 lines
2.3 KiB
Markdown
60 lines
2.3 KiB
Markdown
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# gencpp
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An attempt at simple staged metaprogramming for c/c++.
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This project is not minimum feature complete yet.
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Version 1 will have a most of c and a subset of c++ features available to it.
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## How it works
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A metaprogram is built to generate files before the main program is built. We'll term runtime for this program as `gen_time`. The metaprogram's core implementation are within `gen.hpp` and `gen.cpp` in the project directory.
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`gen.cpp` \`s `main()` will expect to call one `gen_main()` which the user will have to define once for their program. There they will dictate everything that should be generated.
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In order to keep the locality of this code within the same files the following pattern may be used:
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Within `program.cpp` :
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```cpp
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#ifdef gen_time
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#include "gen.hpp"
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...
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u32 gen_main()
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{
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...
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}
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#endif
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#ifndef gen_time
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#include "program.gen.cpp"
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// Regular runtime dependent on the generated code here.
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#endif
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```
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This is ofc entirely optional and the metaprogram can be quite separated from the runtime in file organization.
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## Building
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To fill in.
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## Why
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Macros in c/c++ are usually painful to debug, and templates can be unless your on a monsterous IDE (and even then fail often).
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Unfortunately most programming langauges opt the approach of internally processing the generated code immediately within the AST or not expose it to the user in a nice way to even introspect as a text file. Stage metaprogramming doesn't have this problem, since its entire purpose is to create those generated files.
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This is technically what the macro preprocessor does in a basic form, however naturally its easier to deal with for more complex generation.
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The drawback naturally is generation functions at face value harder to grasp than something following a template pattern (for simple generation). This drawback becomes less valid the more complex the code generation becomes.
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Thus a rule of thumb is if its a simple define you can get away with just the preprocessor, or if the templates being used don't break the debugger, this is most likely not neded.
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However, if the code being generated becomes complex, or from a datatable or database, this will be easier to deal with.
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# TODO:
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* Need problably a better name, I found a few repos with this same one...
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* Actually get to version 1.
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