#type-safety

What Are Kotlin Contracts? If you’ve worked with Kotlin for a while, you’ve likely encountered functions from the standard library that seem to have almost magical powers. Take require() and check()—call them with a condition, and the compiler somehow knows that if execution continues past that line, your variable is no longer nullable. Or use isNullOrEmpty() on a string, and suddenly the…

The Problem: Primitive Obsession You’ve probably seen this pattern in production code: database IDs represented as Long, user emails as String, currency amounts as Double. On the surface, it’s simple and pragmatic. But it introduces a subtle bug vector—primitive obsession. Imagine you have a function that accepts a user ID and a post ID, both as Long: fun deletePost(userId: Long, postId: Long)…

How to: Generic type conversion FROM string

Generic type conversion FROM string

I have a class that I want to use to store “properties” for another class. These properties simply have a name and a value. Ideally, what I would like is to be able to add typed properties, so that the “value” returned is always of the type that I want it to be.

The type should always be a primitive. This class subclasses an abstract class which basically…

How to: Type safety: Unchecked cast

Type safety: Unchecked cast

In my spring application context file, I have something like:

<util:map id="someMap" map-class="java.util.HashMap" key-type="java.lang.String" value-type="java.lang.String"> <entry key="some_key" value="some value" /> <entry key="some_key_2" value="some value" /> </util:map>

In java class, the implementation looks like:

private Map someMap = new HashMap(); someMap =…