Lesson 28 of 55
9 mins readType Synonyms (type) & newtype Wrappers
In Plain English
Use type to create descriptive aliases for existing types (e.g. type Point = (Double, Double)). Use newtype for zero-overhead type-safe single-constructor wrappers.
Deep Dive: How It Works
type Synonyms: type PhoneNumber = String creates a readable alias; interchangeable with String.
newtype Wrappers: newtype USD = USD Double creates a distinct type at compile time that is erased at runtime, guaranteeing zero performance overhead.
Type Safety: newtype prevents accidentally mixing up currencies or measurement units.
Core Rules to Remember
type for Readability: type Matrix = [[Double]] documents complex types clearly.
newtype for Zero-Cost Safety: Guarantees distinct type safety without heap allocation penalty.
Live Interactive Example
Hit Run Code to see it livetype and newtype in Practice
Python 3.12
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Output Console
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How it works: Coord is a synonym for (Double, Double). USD is a distinct newtype.
Your Turn: Micro Challenge
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Micro Exercise
Define CustomerId newtype
- Define `newtype CustomerId = CustomerId Int deriving (Show)`.
- Create `c = CustomerId 1001` and print `"Customer: "` followed by `show c`.
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Sandbox Output
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