While installing Cocoapods, you may have encountered a problem like the following.
ERROR: Error installing cocoapods:
ERROR: Failed to build gem native extension.
current directory: /Library/Ruby/Gems/2.3.0/gems/ffi-1.13.1/ext/ffi_c
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20201118-804-17lxjdu.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
If you have encountered a problem that progresses like this, the solution to the problem is quite simple. If you follow the steps below, you will have resolved this problem.
1. curl -L https://get.rvm.io | bash -s stable
2. rvm install ruby-2.6
3. rvm use ruby-2.6.3
4. rvm --default use 2.6.3
5. sudo gem install cocoapods