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Couplers
All the smells in this group contribute to excessive coupling between classes or show what happens if coupling is replaced by excessive delegation.
A method accesses the data of another object more than its own data.
One class uses the internal fields and methods of another class.
In code you see a series of calls resembling $a->b()->c()->d()
If a class performs only one action, delegating work to another class, why does it exist at all?