Why Does Go Prohibit Taking the Address of Map Values But Allow It for Slices?

Why Does Go Prohibit Address-of Map Values Despite Allowances with Slices?

Many Go users have questioned the prohibition against taking the address of map values, even though slices permit such behavior. One user argued that, like slices, maps are backed by memory structures, but this misconception stems from misunderstandings about the underlying data structures.

Misunderstanding About Maps as Arrays

Contrary to the belief that maps are backed by arrays, they actually rely on bucket-based architectures. Map keys, via an imprecise dynamic hash, determine the primary bucket where both keys and values reside. These elements can be located in overflow buckets as well.

Dynamic Nature of Maps

Maps undergo constant reorganization as entries are added, altered, and removed. This dynamic nature means that map entries do not have fixed memory locations. In contrast, slices are backed by fixed-size arrays, providing stability of addresses.

Why the Prohibition?

The lack of fixed addresses for map values prevents Go from providing a meaningful address for modification. Unlike slices, where modifying elements through addresses is logical, such operations on maps would be unpredictable due to their fluid structure.

Alternative for Modifying Map Elements

To modify map elements in Go, you must retrieve the value, make the necessary changes, and reinsert it into the map. This approach ensures data integrity and prevents unintended consequences that could arise from relying on potentially unstable addresses.

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