Compile-time unit dimension checking - Example

If you have a function that process geo referenced data, it is easy to inadvertently exchange arguments confusing latitude for longitude: in Java they are of type double, defining a custom type we incur in a high friction with the rest of the language.

public static void geoprocessing(double latitude, double longitude) {
    // ...
}

But we can define custom annotation @Longitude and @Latitude and use the checker framework to check consistent usage:

// The function with annotated parameters
public static void geoprocessing(@Latitude double lat, @Longitude double lon) {
    // ...
}

// ...

// We define some variables with unit of measure attached using annotations
@SuppressWarnings("Latitude") @Latitude double lat = 0.0;       // @SuppressWarnings suppress @UnknownUnits warning
@SuppressWarnings("Longitude") @Longitude double lon = 0.0;

// Here the dev inadvertently reversed the arguments and we got a warning
geoprocessing(lon, lat);    // Warning: found @Longitude required @Latitude and viceversa

Checking this code with checker framework generate this:

Warning: found @Longitude required @Latitude

The checker framework has built in unit of measure to do other consistency checking. See the example.