You can write interfaces and for many projects that works fine. There are tools like https://github.com/jacob-carlborg/dstep https://github.com/jacob-carlborg/d

You can write interfaces and for many projects that works fine. There are tools like https://github.com/jacob-carlborg/dstep https://github.com/jacob-carlborg/dstep to convert headers and tools like https://github.com/atilaneves/dpp https://github.com/atilaneves/dpp to "preprocess" the D source to include and translate headers