Any sources? I'm not sure it is that obvious. According to https://adtmag.com/Blogs/WatersWorks/2014/01/Worldwide-Developer-Count.aspx https://adtmag.com/Blogs

Any sources? I'm not sure it is that obvious. According to https://adtmag.com/Blogs/WatersWorks/2014/01/Worldwide-Developer-Count.aspx https://adtmag.com/Blogs/WatersWorks/2014/01/Worldwide-Devel..., in 2014 there were 18 million coders world wide (so few!) of which 11 million were professional and 7.5 million hobbyists. Hobbyists does not have to mean Open Source, but professional does not have to mean proprietary either. At the same time, half of all open source software was written by professionals (http://www.techrepublic.com/article/for-50-percent-of-developers-open-source-is-a-9-to-5-job/ http://www.techrepublic.com/article/for-50-percent-of-develo...). I am not aware that there are any complete stats on how many open source developers exist. And one should not forget that also a professional C++ programmer can use a library as this for a FOSS project. We are getting OT. It is okay to ask with respects to the licence, but it is not okay to act like a GPL project is worthless.