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The entry covers three major topics from this source chunk:

Flyweight Implementation, Proxy Pattern, and Structural Patterns Discussion

Key Concepts:

• Flyweight extrinsic state: GlyphContext uses a BTree to map glyph indices to fonts, proportional to font-change frequency not character count
• GlyphFactory: Lazy-creates and caches 128 Character flyweights by char code; only Characters are shared (Row/Column are not)
• Known Use: InterViews Doc — 180,000 characters needed only 480 objects
• Proxy intent: Surrogate/placeholder to control access
• Four proxy types: Remote, Virtual, Protection, Smart Reference
• Copy-on-write: Proxy defers copying until modification; needs reference counting
• Structural pattern distinctions: Adapter (different interface, retrofit), Bridge (separate hierarchies, up-front), Composite (tree/uniform), Decorator (add responsibilities), Flyweight (share objects), Proxy (same interface, control access)
• Adapter vs Bridge lifecycle: Adapter when incompatibility discovered; Bridge anticipated from start

Implementation highlights: GlyphContext BTree, GlyphFactory lazy creation, ImageProxy virtual proxy, C++ operator-> smart pointer proxy, Smalltalk doesNotUnderstand: generic forwarding (including protection proxy variant)