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Flyweight Pattern

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using System; using System.Collections.Generic; using System.Linq; var pool = new StylePool(); Console.WriteLine(ReferenceEquals(pool.Get("Serif", 16), pool.Get("Serif", 16))); sealed record GlyphStyle(string Font, int Size); sealed record PlacedGlyph(char Letter, int X, GlyphStyle Style); sealed class StylePool { private readonly Dictionary<(string Font, int Size), GlyphStyle> styles = new(); public int Count => styles.Count; public GlyphStyle Get(string font, int size) { var key = (font, size); if (!styles.TryGetValue(key, out var style)) { style = new GlyphStyle(font, size); styles.Add(key, style); } return style; } }

using System; using System.Collections.Generic; using System.Linq; var pool = new StylePool(); Console.WriteLine(ReferenceEquals(pool.Get("Serif", 16), pool.Get("Serif", 16))); // Put only immutable, shareable values in the style object. sealed record GlyphStyle(string Font, int Size); sealed record PlacedGlyph(char Letter, int X, GlyphStyle Style); // Reuse the object for the same key instead of constructing a style per placement. sealed class StylePool { private readonly Dictionary<(string Font, int Size), GlyphStyle> styles = new(); public int Count => styles.Count; public GlyphStyle Get(string font, int size) { var key = (font, size); if (!styles.TryGetValue(key, out var style)) { style = new GlyphStyle(font, size); styles.Add(key, style); } return style; } }

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using System; using System.Collections.Generic; using System.Linq; var pool = new StylePool(); var letters = new[] { new PlacedGlyph('A', 0, pool.Get("Serif", 16)), new PlacedGlyph('B', 20, pool.Get("Serif", 16)) }; foreach (var letter in letters) Console.WriteLine(letter.Letter + "@" + letter.X); Console.WriteLine("styles: " + pool.Count); sealed record GlyphStyle(string Font, int Size); sealed record PlacedGlyph(char Letter, int X, GlyphStyle Style); sealed class StylePool { private readonly Dictionary<(string Font, int Size), GlyphStyle> styles = new(); public int Count => styles.Count; public GlyphStyle Get(string font, int size) { var key = (font, size); if (!styles.TryGetValue(key, out var style)) { style = new GlyphStyle(font, size); styles.Add(key, style); } return style; } }

using System; using System.Collections.Generic; using System.Linq; var pool = new StylePool(); var letters = new[] { new PlacedGlyph('A', 0, pool.Get("Serif", 16)), new PlacedGlyph('B', 20, pool.Get("Serif", 16)) }; foreach (var letter in letters) Console.WriteLine(letter.Letter + "@" + letter.X); Console.WriteLine("styles: " + pool.Count); // Put only immutable, shareable values in the style object. sealed record GlyphStyle(string Font, int Size); sealed record PlacedGlyph(char Letter, int X, GlyphStyle Style); // Reuse the object for the same key instead of constructing a style per placement. sealed class StylePool { private readonly Dictionary<(string Font, int Size), GlyphStyle> styles = new(); public int Count => styles.Count; public GlyphStyle Get(string font, int size) { var key = (font, size); if (!styles.TryGetValue(key, out var style)) { style = new GlyphStyle(font, size); styles.Add(key, style); } return style; } }

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TypeScript example Glyphs share font and size, but retain their own letter and position. Separating those values permits style reuse without mixing one placement’s data into another. // Put only immutable, shareable values in the style object. class GlyphStyle { constructor(readonly font: string, readonly size: number) { Object.freeze(this); } } type PlacedGlyph = Readonly<{ letter: string; x: number; style: GlyphStyle }>; // Reuse the object for the same key instead of constructing a style per placement. class StylePool { private readonly fonts = new Map<string, Map<number, GlyphStyle>>(); get(font: string, size: number): GlyphStyle { let sizes = this.fonts.get(font); if (!sizes) { sizes = new Map(); this.fonts.set(font, sizes); } let style = sizes.get(size); if (!style) { style = new GlyphStyle(font, size); sizes.set(size, style); } return style; } get count(): number { return [...this.fonts.values()].reduce((n, sizes) => n + sizes.size, 0); } } const pool = new StylePool(); const letters: PlacedGlyph[] = [ { letter: "A", x: 0, style: pool.get("Serif", 16) }, { letter: "B", x: 20, style: pool.get("Serif", 16) }, ]; for (const glyph of letters) console.log(glyph.letter + "@" + glyph.x); console.log("styles: " + pool.count); A@0 B@20 styles: 1 Object.freeze keeps the shared style immutable, and the pool looks up both font and size. Retention and size limits are separate policies omitted from this example.

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Each example is a separate .NET 10 console program.

Each C# example is a separate .NET 10 console program. Compile the TypeScript examples for ES2022 or later and run the emitted JavaScript with Node.js.