Chapter 10The Price of AbstractionPaid chapter
Generics — GCShape Stenciling and What Go Actually Does
Understand Go's generic compilation strategy, when generics approach monomorphic performance, and when they don't.
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What this chapter teaches
Common belief
Generics are zero-cost, like C++ templates.
What actually happens
Go uses GCShape stenciling — value types get dedicated code (near-monomorphic), but all pointer types share one body with a runtime dictionary (measurable overhead). It's neither full monomorphization nor type erasure.
Mechanisms covered
Generics over value types give near-monomorphic performance. Generics over pointer types have dictionary overhead but avoid the heap allocation that interfaces cause.
Neither full monomorphization (C++ templates) nor pure type erasure. The result depends on the type parameter shape.
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Escape Analysis — The Compiler's Fragile Decision
Understand how the compiler decides between stack and heap allocation, why the decision is fragile, and how to verify it.
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Maps — Swiss Tables, Growth, and Permanent Memory
Understand the Go 1.24+ Swiss Table map layout, why maps don't shrink, and how to design for memory reclamation.