Stage 1 · Lesson 5 of 8
Polymorphism instead of type checks
means one call works on many types, and each type answers in its own way. Code asks any Shape for its area, and a Circle and a Square each use their own formula. The language picks the right method at run time, which is called dynamic dispatch.
This is what lets you delete long chains of "if the type is X, else if the type is Y". Adding a new type then means adding a class, not hunting for every switch that needs a new branch. Python and TypeScript also allow : if an object has the method, it works, whatever its class.
Common trapkeeping an instanceof or type switch alongside a polymorphic method, so every new type still needs edits in two places.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking the Object Oriented Design Interview
Design Gurus · Intermediate · Subscription
Its opening chapters teach the four OOP ideas applied inside real designs, with UML and running code
- CourseFreeMIT 6.102: Software Construction
MIT · Intermediate
Free MIT readings: Abstract Data Types, Rep Invariants and Interfaces and Subtyping are this stage at university depth