Re: [PATCH 1/8] implement generic key/value map

Jeff King [off-list ref] writes:

It is frequently useful to have a fast, generic data
structure mapping keys to values. We already have something
like this in the "decorate" API, but it has two downsides:

  1. The key type must always be a "struct object *".

  2. The value type is a void pointer, which means it is
     inefficient and cumbersome for storing small values.
     One must either encode their value inside the void
     pointer, or allocate additional storage for the pointer
     to point to.

This patch introduces a generic map data structure, mapping
keys of arbitrary type to values of arbitrary type.

Does the type of keys in a map have to be of the same size, or can a
key of a type with variable size (e.g. struct with a flex member at
the end)?  Same question for the type of values.

Is the type of keys in a map required to have a total order over it,
or is it suffice only to have equality defined?

The latter might matter once we start talking about a huge map that
we may not want to hold in-core.