I found the new value class been

I found the purpose is like :

value class adds attribute to a variable and constraint it’s usage.

I was wondering what is some practical usage of value class.

CodePudding user response：

Well, as stated in the documentation Kotlin Inline classes

Sometimes it is necessary for business logic to create a wrapper around some type. However, it introduces runtime overhead due to additional heap allocations. Moreover, if the wrapped type is primitive, the performance hit is terrible, because primitive types are usually heavily optimized by the runtime, while their wrappers don't get any special treatment.
To solve such issues, Kotlin introduces a special kind of class called an inline class. Inline classes are a subset of value-based classes. They don't have an identity and can only hold values.

CodePudding user response：

A value class can be helpful when, for example, you want to be clear about what unit a certain value uses: does a function expect me to pass my value in meters per second or kilometers per hour? What about miles per hour? You could add documentation on what unit the function expects, but that still would be error-prone. Value classes force developers to use the correct units.

You can also use value classes to provide clear means for other devs on your project on doing operations with your data, for example converting from one unit to another.

Value classes also are not assignment-compatible, so they are treated like actual new class declarations: When a function expects a value class of an integer, you still have to pass an instance of your value class - an integer won't work. With type aliases, you could still accidentally use the underlying type, and thus introduce expensive errors.

In other words, if you simply want things to be easier to read, you can just use type aliases. If you need things to be strict and safe in some way, you probably want to use value classes instead.