Model ordered lists, nested settings, and typed event configuration — Boundary detective

PART I

Warm-up

Reconnect with a useful idea before starting model ordered lists, nested settings, and typed event configuration. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Reject a malformed event without a fake selection

Typed event configuration must connect a declared callback contract to the actual delivery shape. Registration stores a response; delivery supplies inputs later. Shared fnc vocabulary does not make Event, navigator or an arbitrary event field a builtin. Treat every such name as an explicit exercise-host dependency.

Host boundary permits validation before applying events. Required itemId is a positive i32. Supplied deliveries are {itemId:5}, {itemId:0} and {itemId:"five"}. Invalid deliveries preserve selectedId9 and report a targeted error.

Worked reasoning: The first delivery selects5. For independent tests starting at9, zero fails the positive-domain rule and text fails the type rule. Neither should select an invented default id.

Failed alternative: Converting every invalid payload to zero conflates a type defect with a domain defect and may redirect an action to a real record.

Worked reasoning and supplied artifact

Initial each case:selected9
5:i32 positive ->selected5
0:i32 nonpositive ->reject,preserve9
"five":text ->reject type,preserve9

Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.

Try the guided change

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• Write the supplied inputs and initial state before following the example.
• Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
• Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.

PART III

Take a breather

Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.

When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.

PART IV

Independent practice

Project context: Reusable configuration workspace. Build a small, understandable change around model ordered lists, nested settings, and typed event configuration.

Review itemId12, itemId-1 and a missing itemId field with initial selection8. Supply field-specific outcomes and preserved-state evidence.

What to produce

A type/domain/missing-input validation table for event delivery.

• State the intended behavior in a sentence before editing.
• Use only source-backed syntax and the host services whose contract you have been given.
• Record a normal case and a boundary or unavailable-resource case.
• Label hand predictions separately from anything actually measured in a supplied toolchain.

Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.

import wuix.widget;
const button = widget.Button({
    text: "Continue",
    events: {
        click: fnc() -> void {
            navigator.open("dashboard");
        }
    }
});

PART V

Self-check

Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.

You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.

PART VI

Recap & small task

Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.

• Reject a malformed event without a fake selection
• Review itemId12, itemId-1 and a missing itemId field with initial selection8. Supply field-specific outcomes and preserved-state evidence.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Validate shape/type before value-domain rules and preserve prior valid state on rejection.

This marks your personal practice record only. It is not a certification or an official workspace assessment.