Breaking Dependencies - The Visitor Design Pattern in Cpp
summary
Argues the Visitor pattern tradeoff with concrete code and microbenchmarks: classic visitor uses two virtual calls per operation and suffers large slowdowns; a modern std::variant-based visitor uses value semantics, avoids heaps and virtuals, and runs faster in the presented benchmark; an alternate mpark::variant implementation is fastest. Benchmarks run on 10,000 mixed shapes with 2,500 translate operations, tested on GCC and Clang. Also demonstrates an acyclic (dynamic_cast) visitor that is functionally possible but “terribly slow,” so the variant approach works and is recommended.
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chapters (11)
- 0:00The problem with enums
- 12:43Object-oriented solution
- 17:29The classic visitor pattern
- 21:18Visitor pattern in code
- 26:27Modern visitor with variant
- 31:17Modern visitor benefits
- 35:48Performance comparisons
- 39:25Classic vs modern visitor
- 44:25Advanced visitor techniques
- 49:28Visitor pattern summary
- 55:38Q&A session
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