Variables and Ranges

A variable is a container for any value that provides useful operations and a range is a special type of variable with number-specific utilities. While variables and ranges can't "do" anything by themselves, they allow you to create more complicated buttons to bind callbacks to.

Variables

To create a variable, use the variable function, which, like the button function, automatically adds it to the BindingManager. To create a range, use the range function.

val myVariable = variable { "Hello, World" }
val myRange = range { 3.14 }

Variables have several useful operations. Let's first look at map. Map creates a new variable by applying a function to the value of the variable every loop. While this may sound complicated, I assure you it's not. Let's look at an example.

val variable = variable { "World" }
val mappedVariable = variable.map { "Hello, $it" }

println(mappedVariable.get()) // Hello, World

Note that when the value of the initial variable changes, the value of the mapped variable also changes!

There is also mapToRange, which is the same as map but produces a Range. You should generally use this when you're mapping to a numeric value.

Now, let's look at asButton. This function creates a button from the value of a variable and a condition, or predicate. For example:

val leftStickY = variable { gamepad2.left_stick_y }
val button = leftStickY.asButton { it > 0 } // true when left stick y is positive.

Ranges

Ranges are variables with special functions for numbers. Since ranges are variables, all the operations that variables have also work on ranges. In addition, there are some more useful number-specific operations.

First of all, there are built-in asButton functions so that you don't have to do it manually every time. These include:

• greaterThan: returns a button that is true when the value is greater than a number.
• lessThan: returns a button that is true when the value is less than a number.
• atLeast: returns a button that is true when the value is greater than or equal to a number.
• atMost: returns a button that is true when the value is less than or equal to a number.
• inRange: returns a button that is true when the value is within a certain closed range.

There are also built-in map functions:

• deadZone: returns a range that is the same as the original range, but is zero when the value is within a certain threshold of zero.
• invert: returns a range whose value is one minus the original range
• negate: returns a range whose value is the opposite of the original range
• In Kotlin, you can use -range as a shorthand for negate.