Functional error handling

[naleeha]

Things to solve

• Need to be able to return useful error message and UIActions back to the users when failure occurs
• Using Either (scala) or similar Result object that can represent a different type for success vs failure allow returning informative error without having to throw expensive exceptions
• Lots of traits in VUU are intended to be extended by the applications using VUU which can be in Java so cannot use Either on these
• Would be good to use same way to return the failures throughout the codebase (whether only internal to VUU or open to application code)
• Returning Either (so similar concept) enforces by contract that the error cases are considered and handled
• Can chain functions that return the results easily depending on whether it return success or failure - leading to more modular and readable code

Useful references

• For kotlin Result4k library by Nat Pryce solves this by introducing Result (similar to Either but more intuitively named) https://resources.jetbrains.com/storage/products/kotlinconf2019/slides/Friday/Aud%2015/N.Pryce,%20D.McGregor,%20KotlinConf%202019%20-%20Error%20Handling%20Strategies.pdf
• For Java, there is other exiting libraries for this purpose. E.g. functionaljava or vavr

[naleeha]

Potential option 1

Result.scala been introduce as example of how it might look like if VUU had its own Result type defined.

Pros

• compatible with java
• more intuitively named than Either

Cons

• having to re-implement the functions such as map, flatmap
• learning curve as not widely used

Potential option 2

Investigate usage of existing java result libraries