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Add note on value classes vs @newtype #71

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Expand Up @@ -23,6 +23,17 @@ addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.1" cross CrossVersion.fu

For Maven or other build tools, see the Maven Central badge at the top of this README.

## Motivation

This is an alternative to scala's native value classes.

Why this is better than simply `case class Thing(value: String) extends AnyVal`?

That is because value classes [will sometime allocate](https://docs.scala-lang.org/overviews/core/value-classes.html#allocation-summary).
In contratry `@newtype` is allocation free.

For more detailed comparison see https://failex.blogspot.com/2017/04/the-high-cost-of-anyval-subclasses.html

## Usage

For generating newtypes via the `@newtype` macro, see [@newtype macro](#newtype-macro)
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