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2.6 KiB
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46 lines
No EOL
2.6 KiB
HTML
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<head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<title>cancellable — Ludic</title>
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<meta name="description" content="Marks an event whose listeners may veto it with cancel.">
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<link rel="stylesheet" href="base.css">
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<link rel="stylesheet" href="docs.css">
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</head>
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<body>
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<header class="nav"><div class="wrap nav-in"><a class="brand" href="index.html"><span class="logo">L</span> Ludic</a><button class="nav-toggle" aria-label="Toggle menu" aria-expanded="false">☰</button><nav class="nav-links"><a href="index.html">Home</a><a href="api.html">API Reference</a><a class="nav-cta" href="https://git.workshopsoft.io/workshopsoft/ludic">Source ↗</a></nav></div></header>
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<div class="crumbs"><a href="api.html">API Reference</a> <span>›</span> <a href="api.html#events">Events</a> <span>›</span> <span class="here">cancellable</span></div>
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<div class="item-head">
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<span class="kind-badge kind-keyword">keyword</span>
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<h1 id="top">cancellable</h1>
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</div>
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<code class="sig">event cancellable Name { … }</code>
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<div class="desc"><p><code>cancellable</code> marks an event as a <b>decision, not just a notification</b>. A plain event tells listeners something happened; a <code>cancellable</code> event is fired <b>before</b> an action so a listener can veto it by calling <code>cancel</code>. The caller reads the verdict back by using <code>emit</code> as an expression: it yields <code>0</code> when no listener vetoed and <code>1</code> when one did, so the action is applied only on <code>0</code>. This is the Bukkit / DOM <code>preventDefault</code> shape — observation becomes control — and a foreign mod vetoes the same way by setting the payload's trailing cancelled flag over the ABI.</p></div>
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<div class="examples"><h2>Example</h2><pre data-lang="ludic">program CancellableExample {
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event cancellable BeforeHurt { amount: int = 0 }
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var current_health: int = 100
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@On(BeforeHurt) handler AbsorbSmallHits { if amount <= 5 { cancel } }
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handler TakeDamage phase Update {
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if Input.key() == 'h' {
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if emit BeforeHurt(amount: 3) == 0 { current_health = current_health - 3 }
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}
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}
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handler DrawWorld phase Render {
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Screen.clear(Color.MidnightBlue)
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Screen.draw_number(x: 4, y: 4, value: current_health, color: Color.Crimson, scale: 1)
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Screen.show()
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}
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}</pre></div>
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<script>Ludic.highlightAll(); Ludic.installCards(); Ludic.flashTarget();</script>
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