They would also have to make sure no iOS applications make use of symlinks at any point. Since a ipa is simply a zip archive it's possible (and probable) that some applications already make use of symlinks on install or during operation. I think that's the major motivation.
Numerous App Store apps contain symlinks around the detached codesignature, most likely caused by changes over the years to the codesignature utility. Also in keeping with Xcode semantics, embedded frameworks often contain symlinks as well.
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They would also have to make sure no iOS applications make use of symlinks at any point. Since a ipa is simply a zip archive it's possible (and probable) that some applications already make use of symlinks on install or during operation. I think that's the major motivation.
I'm pretty sure symlinks aren't anything any regular xcode ios sdk project would end up delivering in normal use, though.
Plus, old binaries break all the time due to incompatible software or hardware changes (AVFoundation, GL shaders, UDID bans, etc.).
And new builds certainly get new requirements imposed (forced minimum SDK version etc)
Numerous App Store apps contain symlinks around the detached codesignature, most likely caused by changes over the years to the codesignature utility. Also in keeping with Xcode semantics, embedded frameworks often contain symlinks as well.
I've seen people symlink graphics for reuse. For for reusing @2x graphics on iPad, etc.