can not install re2 gem

[travis-pagerduty]

No matter what I try, I keep getting an error when I attempt to install the re2 gem:

checking for main() in -lstdc++... no
checking for stdint.h... yes
checking for rb_str_sublen()... yes
checking for main() in -lre2... yes
checking for re2 requires C++11 compiler... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=~/.asdf/installs/ruby/2.2.4/bin/$(RUBY_BASE_NAME)
        --with-re2-dir
        --without-re2-dir
        --with-re2-include
        --without-re2-include=${re2-dir}/include
        --with-re2-lib
        --without-re2-lib=${re2-dir}/lib
        --with-stdc++lib
        --without-stdc++lib
        --with-re2lib
        --without-re2lib

extconf failed, exit code 1

What am I missing?

[travis-pagerduty]

I had been led to believe that I needed to use gcc5 in order to compile ruby 2.2.4 with asdf. This turned out to be incorrect and I think that may have been the underlying problem. With libssl1.0-dev installed, asdf ruby install 2.2.4 worked and installing the re2 gem subsequently worked without issue (I had installed the re2 library using the instructions on the homepage).