# coders

Every coder has two different encoding modes, though they may share the same implementation:

1. Index key mode, which produces a binary-sortable representation for usage in index building
2. Value mode, which produces a reversible representation for actual data storage

Both modes should result in a Buffer and optionally an auxiliary blob (for out-of-band blob storage).

## Index key mode

Technical priorities and requirements:

- Must be binary-sortable; that is, upon sorting a list of encoded representations, its order *must* match that of the original corresponding inputs if those were to be lexicographically sorted (according to the sorting rules for their data type).
- Must be deterministic; the same input value must result in the same encoded representation every time. If there is a controllable form of non-determinism (eg. a versioned set of sorting rules such as DUCET), it must be possible to regenerate the index keys for all existing values with the new version of the encoding.
- Must be space-efficient.
- Prioritize encoding speed over other (non-required) characteristics such as reversibility.

## Value mode

Technical priorities and requirements:

- Must be reversible; ie. it must be possible to *losslessly* decode the encoded representation back into its original value.
- Must be space-efficient.
- Prioritize *decoding* speed over encoding speed (within reasonable bounds) as well as other (non-required) characteristics such as binary-sortability.