proposal: builtin: Standard library adds interface type for creating a hash

[pjebs]

Proposal Details

This proposal is that:

1. Standard Library creates a new Interface like fmt.Stringer or fmt.GoStringer called builtin.Hasher{ Hash() string}.
2. Where appropriate, all comparable standard library types implement Hasher which returns a unique hash that represents the contents of that type. Ideally, this function remains stable irrespective of how the internals of the type change in the future (except for changes that effect the exported behaviour of the type)

In my use-case:

@bcmills in #6535 asks if reflect.Type is hashable. The response from the Elders is that it is comparable. That was satisfactory for OP.

However for faster comparisons, comparable and hashable are not the same. I suspect having reflect.Type for map keys is not as fast for lookups as a hash of that same reflect.Type for map keys.

[seankhliao]

see #54670

[gabyhelp]

Related Issues

• proposal: go/types: add Hasher{,IgnoreTags} types #69420
• proposal: hash: export a built-in hash function for comparable values #21195 (closed)
• proposal: container/hash: Map, a generic hash table with custom hash function and equivalence relation #69559
• reflect: Is reflect.Type guaranteed to be hashable? #6535 (closed)

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