defcustom :set vs. add-variable-watcher

[Ihor Radchenko]

Hi,

AFAIK, the traditional way to provide side effects to customization
value changes if :set option in `defcustom' definition.

However, it has been suggested [1] that one might also utilize
`add-variable-watcher' for the same purpose.

Given that many users don't actually use customize interface and instead
tend to set variables directly, `add-variable-watcher' looks like a more
reliable option compared to :set.

Are there any reasons to prefer :set over `add-variable-watcher'? Maybe
some non-obvious pitfalls?

[1] https://orgmode.org/list/87h6x8kluc.fsf@localhost

-- 
Ihor Radchenko // yantar92,
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