Common Errors

This page describes the errors you are most likely to encounter when getting started with Komplete Script, and explains what they mean and how to fix them.

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Force-unwrapping a nil optional

What it looks like:

unwrapping a nil value

What it means:

You used the ! operator to force-unwrap an optional, but the value was nil at runtime.

var values = ["a": 0, "b": 1, "c": 2]
var fails = values["missing_key"]! // error — map lookup returns nil

How to fix it:

Check for nil before unwrapping, or use a ternary to supply a fallback:

var result = values["missing_key"] != nil ? values["missing_key"]! : -1

Or restructure to avoid the force-unwrap altogether:

if values["missing_key"] != nil {
    print("Found: \{values["missing_key"]!}")
}

See Optionals for the full unwrapping reference.

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Creating components inside a function

What it looks like:

Components are recreated repeatedly, causing flickering or unexpected resets of state.

What it means:

When you call a function inside a reactive expression (a property, computed state, or component body), Komplete Script tracks the function's arguments as dependencies. Every time those arguments change, the function is called again — and if the function creates components, new component instances are created and old ones are destroyed.

fun make_item(text: String) -> (Component) {
    return Text(text)    // new Text created every time text changes
}

How to fix it:

Use a template instead of a function when producing components. Templates forward their parameters lazily and do not create reactive dependencies on their arguments:

var make_item = template (text: String) {
    Text(text)           // stable — not recreated when text changes
}

See Templates for a detailed explanation of the difference.