Kotlin — Masterclass de Refactorización

★ Un curso de autor de 30 lecciones construido alrededor del catálogo *Refactoring* de Martin Fowler, recontado para Kotlin idiomático. Cada reto te da un snippet realista con olores de código (listas largas de parámetros, strings mágicos, pirámides anidadas de if, guards dispersos, colecciones mutables filtradas) y te pide aplicar un refactor con nombre — Extract Function, Decompose Conditional, Replace Primitive with Object, Replace Loop con `map`, Replace `if` chain con `when`, y 25 más. La feature UX estrella: **cadenas de pistas progresivas**. Cada reto trae 3-6 pasos mecánicos que el botón de pista mágica revela uno por uno, para que un refactor se lea como un checklist granular en vez de un acantilado before-after. Los tests preservan-el-comportamiento verifican cada refactor con stdin/stdout. 30 lecciones · 30 retos · ~120 pistas-paso · termina en un capstone de 5 refactors sobre un validador de orden de sabor a producción.

51 retos64 temas

Cómo funciona1Elige un reto2Lee los requisitos3Programa con IDE4Corre los tests

51 retos

What is refactoring?

Code smells — the catalog of "something's off"

Smell → Refactor reference table

Extract Function

Inline Function

Extract Variable

Inline Variable

Rename Function / Variable / Class

Replace Magic Number with Named Constant

Encapsulate Collection

Move Statements — slide related code together

Move Function — fix Feature Envy

Move Field — relocate state to where it's used

Split Phase — separate parsing from processing

Decompose Conditional

Consolidate Conditional Expression

Replace Nested Conditional with Guard Clauses

Replace Conditional with Polymorphism

Substitute Algorithm — swap the body, preserve the contract

Replace Nullable Chain with Kotlin null-safety

Replace Primitive with Object

Replace Magic String with Enum / sealed class

Combine Functions into Class

Replace Constructor with Factory Function

Extract Class — split a god class along a seam

Parameterize Function

Remove Flag Argument

Preserve Whole Object

Replace Error Code with Result type

Replace Loop with map / filter / sumOf

Split Loop — one pass, one purpose

Replace if-else chain with `when`

Replace setter boilerplate with `apply { }`

Replace `if (x != null)` with `?.let { }`

Replace utility function with extension function

Capstone — Order validation: 5 refactors in sequence

Capstone II — Legacy ETL pipeline: 6 refactors in sequence

Replace Temp with Query

Introduce Parameter Object

Replace Inheritance with Delegation (`by`)

Replace eager chain with a lazy Sequence

Replace try/catch with `runCatching`

Replace mutable state with immutability + `copy`

Replace callback with a returned stream

Replace Conditional Dispatch with a Lookup Map

Replace Accumulator Loop with fold

Replace Nested Loops with flatMap

Replace Temp Plumbing with Scope-Function Chains

Extract Interface to Create a Testing Seam

Replace Boolean+Message Pairs with a Sealed Result

Wrap-up — the refactorer's mindset