When you change a single setting in the IDE to make something more strict and you have 1M+ lines of code, you will get 30K items to fix, via red/yellow/blue squiggles in the IDE. Most of those can be simple refactorings, but the performance & UI of the IDE makes it incredibly unwieldy and it will sometimes fight you back, sometime crash internal processes which leave refactorings half baked and so. Now imagine you change 50 such settings, to make the compiler force you to write better code. Changing 200K+ lines of code yourself is a nightmare (and to prove it still does the same thing afterwards). Instead, claude systematically approaches whole classes of errors and convert them to cleaner variants (either using our custom skills or it writing new scripts to do it). I consider myself an advanced user of IDE's, know how to do bulk refactoring and renames and so on (esp with JetBrains tools), and I would say it would be a near impossible task to do as a human. Then there are other developers - so you flip a setting and now 5 other people's IDE's are forcing them to work a specific way which will make you unpopular very quickly and revert the changes. So, since most of us no longer use IDE's as our main tool to build/diagnose, we can more easily flip compiler settings without destroying someone else's week. Hope that makes sense.
Oh it also helps to split refactoring work into three buckets: business logic changes, performance changes (same output as before but faster) and cosmetic changes (rename files/folders/classes, breaking large files up, add logging/comments, domain layering etc). We tend to focus on performance and cosmetic changes for bulk refactors and leave logic changes to more dedicated sessions as to avoid changing what the system do (our domain is fairly complex and we cannot afford breakages). We also managed to port ALL of our code to dotnet 10 lts and have clean boundaries between projects (we have a mono-repo with about 50 projects in it), so we can wholesale upgrade dependencies without a sweat.
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When you change a single setting in the IDE to make something more strict and you have 1M+ lines of code, you will get 30K items to fix, via red/yellow/blue squiggles in the IDE. Most of those can be simple refactorings, but the performance & UI of the IDE makes it incredibly unwieldy and it will sometimes fight you back, sometime crash internal processes which leave refactorings half baked and so. Now imagine you change 50 such settings, to make the compiler force you to write better code. Changing 200K+ lines of code yourself is a nightmare (and to prove it still does the same thing afterwards). Instead, claude systematically approaches whole classes of errors and convert them to cleaner variants (either using our custom skills or it writing new scripts to do it). I consider myself an advanced user of IDE's, know how to do bulk refactoring and renames and so on (esp with JetBrains tools), and I would say it would be a near impossible task to do as a human. Then there are other developers - so you flip a setting and now 5 other people's IDE's are forcing them to work a specific way which will make you unpopular very quickly and revert the changes. So, since most of us no longer use IDE's as our main tool to build/diagnose, we can more easily flip compiler settings without destroying someone else's week. Hope that makes sense.
Oh it also helps to split refactoring work into three buckets: business logic changes, performance changes (same output as before but faster) and cosmetic changes (rename files/folders/classes, breaking large files up, add logging/comments, domain layering etc). We tend to focus on performance and cosmetic changes for bulk refactors and leave logic changes to more dedicated sessions as to avoid changing what the system do (our domain is fairly complex and we cannot afford breakages). We also managed to port ALL of our code to dotnet 10 lts and have clean boundaries between projects (we have a mono-repo with about 50 projects in it), so we can wholesale upgrade dependencies without a sweat.