Clean Architecture

I n fo r m ati o n H i d i n g
The 
FinancialReportRequester
interface serves a different purpose. It is 
there to protect the 
FinancialReportController
from knowing too much 
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Conclusion
75
about the internals of the 
Interactor
. If that interface were not there, then the 
Controller
would have transitive dependencies on the 
FinancialEntities
.
Transitive dependencies are a violation of the general principle that software 
entities should not depend on things they don’t directly use. We’ll encounter 
that principle again when we talk about the Interface Segregation Principle 
and the Common Reuse Principle.
So, even though our first priority is to protect the 
Interactor
from changes to 
the 
Controller
, we also want to protect the 
Controller
from changes to the 
Interactor
by hiding the internals of the 
Interactor
.
C o n c lu s i o n
The OCP is one of the driving forces behind the architecture of systems. 
The goal is to make the system easy to extend without incurring a high 
impact of change. This goal is accomplished by partitioning the system into 
components, and arranging those components into a dependency hierarchy 
that protects higher-level components from changes in lower-level 
components.
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77
9
L S P: Th e L i s kov 
S u bstitution 
Pr i nc i ple
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