C++ Template preprocessor tool

Question

Is there a compiler or standalone preprocessor which takes C++ files and runs a template expansion pass, generating new C++ code with expanded template instantiations?

I remember such a tool in the mid-90s when templates were still new and experimental, and the preprocessor was a way to do template programming with compilers without native template support.

This is a lot more complicated than a macro-processing step since it would likely require parsing and tokenizing the code to understand the contexts.

My hope is to use such a tool when writing OpenCL code. OpenCL is C++, but does not support templates. I'm hoping I can write templates, even simple ones like with integer or bool only arguments, and have some tool pre-parse the file and go through and find the use of the templates and expand the invocations and give me new C++ code that the OpenCL compiler can understand.

Even a very limited tool could be useful, it does not need to support every template quirk, nor even support multiple modules or anything.

The alternative: #define macros everywhere.. uglier, unsafe, less efficient, and less versatile.

Answer 1

Why not take a look at GCC's C++ compiler? I'm sure with a bit of effort you can hijack the compiling process and simply dump the "expanded" templates into their own code files. However, writing this yourself would be fairly simply, I would imagine. I don't see why you need a "full" compiler in order to accomplish this at all. From my experience, templates only are aware of the context in instances where the compiler wants to give you an error. If you validate your template code before-hand with a real compiler, then run it though a "search/replace" tool, you will get valid code; I'm sure.

Answer 2

There is no such tool - templates are part of the language, not some pre-processor pass - they are processed by the compiler, just like other code.

Answer 3

Comeau C++ can "compile" C++ to C. This would seem to be close to your goal, as OpenCL does not support C++ – it's much closer to C.