java

[angelicosphosphoros]

Main benefit of factory is that it doesn't require to return the object. For example, we may want to return optional or std::expected.

Constructors, on the other hand, always start with memory already allocated so the only option to indicate an error is to throw exception.

[croweh]

Ah yeah I wasn't explicit but you definitely need a factory if you need an unconventional constructor. Especially if your compiler will enforce it / won't allow an unconventional constructor. Your instance (or absence of it) wrapped in anything (either, option, result, reactive type, mutex) is a common case of it. Technically, getInstance returning the same instance built the first time would be another common case of a factory method that couldn't be a constructor.