What exactly do you mean by “Shell scripts”? If the script contains a proper Shebang you can easily run it via `./script.sh`. If not you use: `bash ./script.sh`.
Admittedly for the description given, it does sound like CDPATH would work. But I'm going to assume there's a reason, and functions that change the current working directory are the perfect example of functions that can not be run in a subshell, so will have to be rewritten to fish, which is what the author was providing.
$ export cdc_stuff='/Users/me/src/project_stuff'
$ cd $cdc_stuff
in the event you're looking for alternatives, perhaps porting your code to (e.g.) ruby could work.
just in case, here's the isbn number of a book called, 'Build Awesome Command-Line Applications in Ruby 2,' from the pragmatic bookshelf: 978-1-93778-575-8
https://github.com/rupa/z (bash, zsh)
https://github.com/sjl/z-fish0: https://github.com/huyng/bashmarks 1: https://github.com/techwizrd/fishmarks
What I meant in my comment above is a lot of 'download an install' instructions in tutorials, and sometimes installation wizards for programs are written for bash, and can't be run without modification in Fish. Not a major setback, but for a Bash user it would just work.