Generics

Go 12 Sep 2026 4 min read

Merge Map Entries with maps.Copy in Go

Merging two Go maps often comes down to one precise rule: entries from one map are assigned into another, and matching keys replace existing destination values. maps.Copy gives that operation a standard-library form without changing its underlying assignment semantics. The function mutates the destination map. It does not allocate a replacement, return a merged value, or recursively copy data stored behind pointers, slices, maps, or other reference-bearing values. Source entries overwrite matching destination keys maps.Copy accepts a destination followed by a source. Every source pair is assigned to the destination. Keys that exist only in the destination remain present.

Go Maps

Go 12 Sep 2026 4 min read

Filter Map Entries in Place with maps.DeleteFunc

Filtering a Go map often means removing entries from an existing map rather than allocating a replacement. maps.DeleteFunc expresses that operation directly: it visits entries and deletes each pair for which a predicate returns true. That mutation model is the central detail. The function does not return a filtered copy, and callers that share the same map observe the deletions. The predicate receives both key and value maps.DeleteFunc accepts a map and a function with the key and value types of that map. A compact filter can use either argument or both:

Go Maps

Go 12 Sep 2026 5 min read

Compare Map Values with maps.EqualFunc in Go

Two Go maps can represent the same logical data even when their value types differ or their values need domain-specific comparison. maps.EqualFunc handles that case by matching keys normally while delegating value comparison to a caller-supplied function. That split matters. The comparator controls value equivalence only. It cannot redefine key identity, compensate for a missing key, or make maps with different entry counts equal. Key membership is checked before value equivalence The function accepts two maps with the same key type but potentially different value types:

Go Maps

Go 12 Sep 2026 4 min read

Clone Go Maps with maps.Clone

A Go map variable refers to mutable map state. Assigning that variable to another variable does not create an independent map: writes through either name affect the same map. When code needs a separate top-level map with the same entries, maps.Clone makes that boundary explicit. The function is deliberately narrow. It copies map entries using ordinary assignment. The resulting map can be changed independently at the key-value entry level, but reference-like data stored inside keys or values can still share underlying state.

Go Maps