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Contexts and Indexing

What You Receive in init/step!/cleanup

Entity methods receive a SubContextView, not the raw ProcessContext.

That view exposes:

  • local subcontext variables,
  • routed/shared variables,
  • globals via getglobals(context).

Reading Variables

function Processes.step!(::MyAlgo, context)
    (; state, dt) = context
    # ...
    return (;)
end

context.name and destructuring both map to generated view lookups.

Writing Variables

Return a NamedTuple from step!/init/cleanup.

  • Existing names update mapped targets.
  • New names are added to local subcontext.
  • Type changes are rejected at merge time for stability.

Top-Level Context Access

From a process:

ctx = getcontext(p)

From a context, index by:

  • symbol key: ctx[:Fib_1]
  • registered value/type: ctx[Fib], ctx[Fib()], ctx[my_unique_fib]

This behavior comes from ProcessContext.getindex(pc, obj) resolving through the registry key.

Related symbol-based lookup also works on resolved loop algorithms and registries:

resolved = resolve(CompositeAlgorithm(Fib, Noise, (1, 2)))
reg = getregistry(resolved)

resolved[:Fib_1]   # same object as resolved.Fib_1
reg[:Fib_1]        # registered IdentifiableAlgo
ctx[:Fib_1]        # subcontext

Use loop-algorithm indexing when you want the registered algorithm/state object, and context indexing when you want its current subcontext data.

Re-Initializing One Subcontext

You can re-run init for one registered algorithm inside an existing context:

ctx = initcontext(resolved)

ctx = initcontext(ctx, :Fib_1)
ctx = initcontext(ctx, :Fib_1; inputs = (; seed = 123))
ctx = initcontext(ctx, resolved[:Fib_1]; overrides = (; value = 0.0))

This updates only the targeted subcontext.

  • inputs are merged into that subcontext before init(...) runs.
  • overrides are merged into that subcontext after init(...) returns.

Globals

ProcessContext includes a globals field.

Common globals used internally:

  • lifetime
  • algo
  • process (in runtime loop context)

Use getglobals(context) inside entity methods when you need them.

You can also select globals with Var(:name) in APIs like Processes.Until(...). See Vars (Var Selectors).