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45 lines
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2.7 KiB
HTML
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<title>event — Ludic</title>
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<meta name="description" content="Declare a public event carrying a flat payload that listeners react to.">
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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">event</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">event</h1>
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</div>
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<code class="sig">event Name { field: T = default }</code>
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<div class="desc"><p><code>event</code> declares a public event — a named signal carrying a flat payload of typed fields (each with a default; the payload may be empty). Where lifecycle hooks are the closed reactions the author compiles in, events are the <b>open runtime surface a game exposes to mods</b>: an in-language listener registers with <code>@On(Name)</code> and reads the payload fields by name, and <code>emit Name(field: value, …)</code> fires every listener in declaration order as a direct call. It all desugars to a generated function — there is no interpreter and no dispatch table — and a program that declares no <code>event</code> compiles byte-for-byte as before. Mark an event <code>cancellable</code> when a listener should be able to veto the action it announces.</p></div>
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<div class="examples"><h2>Example</h2><pre data-lang="ludic">program EventExample {
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event EnemyDefeated { points: int = 0 }
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var score: int = 0
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@On(EnemyDefeated) handler AddScore { score = score + points }
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@On(EnemyDefeated) handler PlayChime { Screen.status("enemy down") }
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handler ScoreOnKey phase Update {
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if Input.key() == 'k' { emit EnemyDefeated(points: 10) }
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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: score, color: Color.Gold, scale: 1)
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Screen.show()
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}
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}</pre></div>
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