Indexing for array values

[joeltio]

This issue keeps track of design decisions for adding a way to index arrays in protobuf.

The main things to figure out are:

• Mutating specific value in multi-dimensional array
• Retrieving value in multi-dimensional array

[joeltio]

Proposal: Lens-like mutations and ValueRef

1. Lens-like mutations

All mutations will be done by first retrieving the value to mutate, then changing the value. This will correspond to:

mutateOp(retrieveOp(attrRef), newVal)

The purpose of this is to delegate referencing values all to the retrieveOp. So we only have AttributeRef in one place.

This design is based off functional lenses.

2. ValueRef over AttributeRef

The usages of AttributeRef (graph mutateOp and retrieveOp, services get and set attribute) often refer to a value instead of an attribute. We want to modify a certain value or retrieve a certain value, not so much that we intentionally want to change an attribute.

I propose to add a ValueRef in place of existing AttributeRef usages. The ValueRef will look something like:

message ValueRef {
  // Which component to retrieve the value
  AttributeRef attr = 1;
  // A list of indexes
  repeated int64 attr_indexes = 2;
}

For an attribute that is a primitive (non-array), the indexes will be empty.

[mrzzy]

All mutations will be done by first retrieving the value to mutate, then changing the value.

What happens when only one element out of a large array is updated? Would it cause a full rewrite of the entire array?

2. ValueRef over AttributeRef

Looks good 👍 , although we should probably disambiguate between Array indexes and index in ICS.

[joeltio]

All mutations will be done by first retrieving the value to mutate, then changing the value.

What happens when only one element out of a large array is updated? Would it cause a full rewrite of the entire array?

Nope. As mutateOp calls retrieveOp which uses ValueRef, we can pinpoint the exact value to update in the array to update.

Looks good +1 , although we should probably disambiguate between Array indexes and index in ICS.

Yeah, but it seems like only the engine needs to disambiguate for now. The protobuf definitions have no idea of an ICS index.

[mrzzy]

Yeah, but it seems like only the engine needs to disambiguate for now. The protobuf definitions have no idea of an ICS index.

How about attr_indexes or array_indexes?

[joeltio]

Ok, I think attr_indexes will be better:

  // Which component to retrieve the value
  AttributeRef attr = 1;
  // A list of indexes
  repeated int64 attr_indexes = 2;
}

[mrzzy]

Seems like ValueRef is destined to replace AttributeRef so maybe it makes sense to merge them together:

message ValueRef {
  // id of the entity to the retrieve from
  uint32 entity_id = 1;
  // Name of the component type to retrieve from entity
  string component = 2;
  // Name of the attribute to retrieve from component
  string attribute = 3;
   // A list of indexes
  repeated int64 attr_indexes = 4;
}

indexes remain unset for primitive values.