Looking closer at composable functions

The UI of a Compose app is built by writing and calling composable functions. We have already done both in the previous chapters, but my explanations regarding the structure of a composable, as well as its internals, have been quite basic—it’s time to fix that.

Building blocks of composable functions

A composable function is a Kotlin function that has been annotated with @Composable. All composables must be marked this way because the annotation informs the Compose compiler that the function converts data into UI elements.

The signature of a Kotlin function consists of the following parts or building blocks:

• An optional visibility modifier (private, protected, internal, or public)
• The fun keyword
• A name
• A list of parameters (can be empty) or, optionally, a default value
• An optional return type
• A block of code

Let’s explore these parts in greater detail.

The default visibility...