Review event and capability lifetimes — Build the smallest useful slice

PART I

Warm-up

Reconnect with a useful idea before starting review event and capability lifetimes. 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

Make a callback’s required context explicit

A host event callback renders product updates into panelP. The panel can close before an asynchronous data response arrives. The host has not specified callback capture or validity semantics.

List the required context rather than assuming the closure keeps every native handle safe. The response needs request identity, a currently valid destination and permission at use. If panelP is no longer valid, the host must reject or redirect the update under a documented policy. A language-level anonymous fnc illustration does not define native handle retention or cancellation behavior.

This is a supplied exercise-host design contract. WillowScript and these cross-library integrations remain proposed and unimplemented here. The trace is a hand prediction or supplied observation for analysis, never a claimed script run. No cancellation method, WDB transaction API, permission manifest or native lifetime mechanism is invented.

Worked reasoning and supplied artifact

// Design artifact; not executable WillowScript.
// A host event callback renders product updates into panelP. The panel can close before an asynchronous data response arrives. The host has not specified callback capture or validity semantics.
// 1. Register whileP valid.
// 2. P closes before response.
// 3. Late response must check the agreed destination/identity contract, not assume permanent validity.

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: Independent integration rehearsal. Build a small, understandable change around review event and capability lifetimes.

Write a callback context contract with valid-destination,closed-destination and changed-selection rows, identifying unresolved host guarantees.

What to produce

Write a callback context contract with valid-destination,closed-destination and changed-selection rows, identifying unresolved host guarantees.

• 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.

• Make a callback’s required context explicit
• A host event callback renders product updates into panelP. The panel can close before an asynchronous data response arrives. The host has not specified callback capture or validity semantics.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain the decision in “Make a callback’s required context explicit” using the supplied case, then state one input change that would invalidate your conclusion.

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