expect/actual 类与属性

expect/actual is not limited to functions. You can also declare whole classes, properties, and even objects that differ per platform.

Need a value that each platform defines? Declare an expect val in commonMain and let every target supply the actual value.

Android and iOS each provide an actual val. The property reads like a constant in shared code but resolves per platform.

For richer behavior, declare an expect class. It lists the members shared code can use, while each platform fills in the bodies.

The androidMain actual class implements every declared member. Here name returns an Android-specific string.

Each actual class must declare every member the expect promised, with the same names and types. Missing one is a compile error.

If the expect class has a constructor, mark the platform one as an actual constructor. The compiler checks that they line up.

In shared code you just create and use it. The right actual backs the object, so common logic stays unaware of the platform.

An actual class may add extra private members beyond the expect. Only what the expect declares is visible to shared code.

Use an expect property for a value, an expect function for an action, and an expect class only when you need state plus behavior. ✨

Recent Kotlin nudges you toward interfaces plus expect/actual functions over expect classes, but classes still work well today.

You saw that expect/actual covers properties and classes too. Declare the shape in commonMain, then fulfill every member in each platform's actual. 🎉