After 112 episodes, Michael can’t introduce the show, Allen pronounces it “ma-meee”, and don’t make Joe run your janky tests as The Pragmatic Programmer teaches us how we should use exceptions and program deliberately.
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When to use Exceptions
- In an earlier chapter, Dead Programs Tell No Lies, the book recommends:
- Checking for every possible error.
- Favor crashing your program over running into an inconsistent state.
- This can get really ugly! Especially if you believe in the “one return at the bottom” methodology for your methods.
- You can accomplish the same thing by just catching an exception for a block of code, and throwing your own with additional information.
- This is nice, but it brings up the question? When should you return a failed status, and when should you throw an exception?
- Do you tend to throw more exceptions in one layer more than another, such as throwing more in your C# layer than your JS layer?
- The authors advise throwing exceptions for unexpected events.
- Ask yourself, will the code still work if I remove the exception handlers? If you answered “no”, then maybe your throwing exceptions for non-exceptional circumstances.
- Use exceptions for exceptional problems
Exceptions vs Error Handling
- Should you throw an exception if you try to open a file, and it doesn’t exist?
- If it should be there, i.e. a config, yes, throw the exception.
- If it might be OK for it not to be there, i.e. you’re polling for a file to be created, then no, you should handle the error condition.
- Is it dangerous to rely on implicit exception throwing, i.e. opening a file that isn’t there?
- On the one hand, it’s cleaner without checking for the exceptions, but there’s no signaling to your co-coders that you did this intentionally.
- Exceptions are a kind of coupling because they break the normal input/output contract.
- Some languages / frameworks allow you to register error handlers that are outside the flow of the normal problem.
- This is great for certain types of problems, like serialization problems, particularly when there is a prescribed flow, such as error pages, serialization, or SSL errors.
Programming by Coincidence
- What does it mean to “program by coincidence”?
- Getting lured into a false sense of security and then getting hit by what you were trying to avoid.
- Avoid programming by coincidence and instead program deliberately. Don’t rely on being lucky.
- Writing code and seeing that it works without fully understanding why is how you program by coincidence.
- This really becomes a problem when something goes wrong and you can’t figure out why because you never knew why it worked to start off with.
- We may not be innocent …
- What if you write code that adheres to some other code that was done in error … if that code is eventually fixed, your own code may fail.
- So if it’s working, why would you touch it?
- It might not actually be working …
- Maybe it doesn’t work with a different resolution.
- Undocumented code might change, thus changing your “luck”.
- Unnecessary method calls slow down the code.
- Those extra calls increase the risk of bugs.
- It might not actually be working …
- Write code that others implement with well documented code that adheres to a contract.
Accidents of Context
- You can also make the mistake that you assume certain things are a given, such as that there’s a UI or that there’s a given language.
- Don’t assume something, prove it.
- Assumptions that aren’t based on fact become a major sticking point in many cases.
- Don’t Program by Coincidence
How to Program Deliberately
- Always be aware of what you’re doing.
- Don’t code blindfolded, Make sure you understand what you’re programming in, both business domain related and programming language.
- Code from a plan.
- Rely on reliable things. Don’t code based on assumptions.
- Document assumptions.
- Test your code _and_ your assumptions.
- Prioritize and spend time on the most important aspects first.
- Don’t let old code dictate new code. Be prepared to refactor if necessary.
Resources We Like
- The Pragmatic Programmer by Andrew Hunt, David Thomas (Amazon)
- The Pragmatic Bookshelf (pragprog.com)
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- OMG! It’s here! Oh mother… the ON-AIR VERSION!!! | Family Feud (YouTube)
- Thunder Talks (episode 87)
- Spotify engineering culture (part 1) (labs.spotify.com)
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