Step by Step:

• Create a new project: cargo new rs_workshop
• Add a new Crate dependency: cargo add clap --features derive

Commit 1: Start of Work

• Add Clap using the Derive API
  • Add the CLI - The parser for the arguments sent to the application and core component
  • Add a Subcommand enum, the different command, or program, values which our application can expect
  • Add an Args struct, a collection of arguments for each individual subcommand that our application can expect
• Add a command for addition and subtraction
• Show naive solution, show solution with less code-duplication

Commit 2: Closures

• Break args out
• Create methods for add and sub
• Create a variable, func, which is a closure that is set to either add or sub

Commit 3: Unit Tests

Now that closures have been added, functions are outside the scope of main

• Unit test the add and sub functions
• Explain the nuance of unit tests:
  • In Rust, unit tests are in the same source file as our implementation
  • Use super::*
  • They are in a separate module, decorated with #[cfg(test)]
    • This means they will not be compiled into our executable binary if we are not compiling with the test flag enabled
  • Tests inside the module are decorated with #[test]
    • This is used by the test runner to determine what code is meant to be tested.

Commit 4: Generics

• Take existing functions, add generic parameters for T and R
  • T stands for Type, R stands for Return
• Add generic type constraints for std::ops::Add<Output = R> and std::ops::Sub<Output = R>

Commit 5: REPL

Running our application repeatedly is hard, and makes using the calculator unintuitive.

• Add a function for reading from stdin
• Loop in the main method
• Add #[command(multicall = true)] to Cli
• Convert Cli::parse to Cli::try_parse_from()
• Add a command for exiting
• Add error handling (print the error)

Commit 6: Accumulator

• Add an accumulator which is a std::cell::RefCell
• Instead of answer, use acc
• Mutate the interior value of acc between loops
• Make y value an option