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 shape-based stenciling and dictionaries. Pointer types can share a body; value instantiations can also receive dictionaries. Actual overhead depends on operations, inlining, and call sites.

Mechanisms covered
Generic and concrete paths may perform similarly after optimization. Neither generic pointer arguments nor interface arguments imply an unconditional allocation or dispatch cost.
Neither full monomorphization (C++ templates) nor pure type erasure. The result depends on the type parameter shape.
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