After reading Clean Architecture, I've had a trouble understanding differences of each programming paradigm;

• Structured Programming (SP)
• Object-oriented Programming (OOP)
• Functional Programming (FP)

Let me share a summary of  Clean Architecture Part II, Starting with the Bricks: Programming Paradigms.

Firstly, what is,

A Programming Paradigm?

It is a programming discipline, used to decide which form of programming structure (SP, OOP, FP) to use.

Each paradigm places a constraint on a programmer.

NOTE: "Paradigm" is pronounced as par-uh-dahym NOT as par-uh-dig-uhms.

Disciplines imposed by each paradigm

• Structured Programming

  A direct transfer of control Example: goto statement is discouraged or removed. Instead of using a goto statement for an unconstrainted control flow, programmers are forced to use (now familiar) constructs such as if/else, for/while loops.

• Object-oriented Programming

  An indirect transfer of control Example: Function pointers are eliminated. OOP provides a plug-in architecture with a use of polymorphism. Polymorphism also enables a programmer to change the code dependencies with Dependency Inversion Principle.

• Functional Programming

  A variable assignment Example: Cannot assign a new value to a variable.

What problem(s) each paradigm solves

• Structured Programming

  SP causes noodlers (preventing spaghetti codes) to become an endangers species How?  By discouraging the use of goto and encouraging functional decomposition and use of data structures.

• Object-oriented Programming

  Complete control over code dependencies and flows. How? By using dependency inversion with the use of polymorphism.

• Functional Programming

  All race/deadlock conditions, and concurrent update problems. How? Problems mentioned above are caused by variable mutation. FP prevents variable assignment, thus those problems can't occur.

Programming Paradigm Use Cases

Initially, I thought about when to use each paradigm. When you consider a software architecture as a whole, it makes more sense to use each one appropriately.

So as an example, write low-level methods with SP principles, and separate immutable components (written with FP) from mutable components to mitigate resource contention and control flows with OOP.

Surprises 🎉

1. Science theories and laws are not provable, only falsifiable.
2. Encapsulation, Inheritance, and Polymorphism concepts are not introduced in OOP! - These concepts were available in C, but the usages were unsafe and OOP made it safer/easier to use.
3. Access modifiers, public``private and protected in OOP are just a hack necessitated by technical reasons! - C header files hid member variables but C++ header files had to expose member variables because C++ compilers have to know the size of the instances of each class. Even worse, modern OOP languages such as C#/Java do not separate a class declaration from its implementation therefore, those modifiers are necessary evils.
4. In FP, variables do NOT vary!

Conclusion

1. Each paradigm tells a programmer what NOT to do.
2. Clean Architecture is a book written by Robert C. Martin, aka Uncle "Bob".
3. Coding Blocks guys talk about it in more detail in Episode 69 – Clean Architecture – Programming Paradigms.