Koshin StudioA function named “load from iCloud if newer” compared nothing: a 20-record history could become 1
Development log of the Toreca Dash app / August 2026
My iPhone app Toreca Dash has a record of applications that users build up themselves: which lotteries they entered and how they turned out. It is a personal record built by hand, and once lost it cannot be recovered.
On 23 August 2026 I read a file I had not yet reviewed (1,076 lines) and found a path where this record could vanish entirely. It began with trusting a function’s name.
Written from my work log of 23 August 2026.
The name says “if newer”; the body compares nothing
The function that syncs with iCloud was named loadFromICloudIfNewer: “load from iCloud if it is newer”. But the body never checked whether anything was newer; whenever iCloud changed, it replaced everything with that content.
What can happen:
- Device A has 20 records (and so does iCloud).
- Device B is installed fresh. iCloud’s first sync is asynchronous, so just after launch the records may be empty.
- On device B, one record is added, and saving overwrites iCloud with [1 record].
- Device A receives the change notice and goes from 20 records to 1 (19 lost).
The code had an export/import feature, described as being “to prevent all data vanishing when you change phones”. The author knew this area was fragile.
The fix: compare update times, and never overwrite with empty
- Store an update time (
entriesUpdatedAt) on both device and iCloud, and import only when the other side is newer, so the function does what its name says. - Even for old data with no time yet, always prevent overwriting with empty content.
- On the first restore on a new device, inherit iCloud’s time.
What I learned
A function’s name may state the spec, but the body may not match.
- Do not trust names; read the body. “IfNewer” compared nothing.
- Be extra suspicious of writes to data that cannot be recovered. A record built by hand does not come back.
- “Empty” is a dangerous value. Make “never overwrite with empty” the last line of defence.
- First sync is asynchronous. Empty right after launch does not mean no data.
- Read the unreviewed files. Large, old files hide the most.
This is the English version of the original Japanese article.
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