golang-data-structures

Use make([]T, 0, n) for slices and make(map[K]V, n) for maps when the size is known or estimable. Preallocation avoids repeated backing-array copies during slice growth and rehashing during map population. Go 1.21+ also offers slices.Grow for pre-growing before bulk appends.

Use strings.Builder for pure string concatenation because String() returns the result without copying. Use bytes.Buffer when you need io.Reader or io.Writer interfaces for bidirectional I/O. Both support Grow(n) for preallocation.

Go maps never shrink their bucket array; delete() removes entries but the allocated bucket memory is retained. The only fix is rebuilding: create a fresh map with make and copy surviving entries, or set the map to nil and reassign so the GC can reclaim it.

Use map[K]*V for large structs since map access copies the entire value on every read. For small structs under roughly 128 bytes, value maps are typically faster because pointer maps add GC pressure and indirection cost.

Avoid generics for single concrete types, any-constrained functions that just reimplement interface{}, or cases with two or fewer instantiations. Generics add value for containers, algorithms, and utilities where identical logic applies across types, not for serialization helpers.

weak.Pointer[T], available since Go 1.24, holds a reference without preventing garbage collection; Value() returns nil after the object is collected. Use it for deduplication caches and canonicalization maps, paired with runtime.AddCleanup instead of the more error-prone SetFinalizer.