How to check if a variable has been assigned a variable in AutoHotKey?

Question

How might one check if a variable exists before using it? For example, you might have an Object that can contains 36 keys, one for each alphanumeric character, and you want to set another variable to the value of the key you selected.

Answer 1

This code could look like this:

myObject := {} ; Create myObject

; Some other code here, possibly that adds key-value pairs to the Object

getInput := InputHook("L1") ; Create an InputHook to intercept one character
getInput.Start() ; Start the InputHook
getInput.Wait() ; Wait for a character input

myVar := myObject.%getInput.Input% ; Set myVar to the pressed key in myObject

This code would work, unless the key that was entered doesn't exist, in which case an error will be thrown. In order to avoid that situation, we can add turn myVar := myObject.%getInput.Input% into a Try statement. Now, our code will look like this:

myObject := {} ; Create myObject

; Some other code here, possibly that adds key-value pairs to the Object

getInput := InputHook("L1") ; Create an InputHook to intercept one character
getInput.Start() ; Start the InputHook
getInput.Wait() ; Wait for a character input

Try myVar := myObject.%getInput.Input% ; Set myVar to the pressed key in myObject
Catch
    myVar := "" ; If pressed key in myObject doesn't exist, set myVar to empty value

Now, if the pressed key is not a key existing in myObject, then myVar will be set to an empty value. The catch statement is not required, but including it means that any future operations on myVar will have a value to operate on.

You can find more information on Try-Catch statements on the AutoHotkey Docs.