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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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