Context Internals

The runtime data stack is:

1. ProcessContext
2. SubContext
3. SubContextView

1. ProcessContext

ProcessContext{D,Reg} holds (src/Context/StructDefs.jl):

• subcontexts::D: named tuple of subcontexts plus globals.
• registry::Reg: a NameSpaceRegistry used for static routing and lookup.

Access patterns (src/Context/ProcessContexts.jl):

• pc[:name] or pc.name by subcontext symbol.
• pc[obj] by algorithm/state value/type (resolved through registry key).

globals is a regular field in subcontexts; runtime code injects process-level values there (like process, lifetime, algo).

2. SubContext

SubContext{Name,Data,SharedContexts,SharedVars} stores (src/Context/StructDefs.jl):

• data::NamedTuple: local variables owned by that entity.
• sharedcontexts: whole-context sharing metadata (Share).
• sharedvars: variable routes metadata (Route).

Initialization builds empty SubContexts for every registry key, then fills them by init.

3. SubContextView

step!, init, and cleanup run against a SubContextView (src/Context/View/StructDef.jl).

A view carries:

• the full context,
• the current identifiable instance,
• optionally injected locals.

Property access is generated through VarLocations (src/Context/View/Locations.jl):

• local vars,
• shared-context vars,
• routed vars,
• injected vars.

Name precedence for reads:

1. shared vars
2. routed vars
3. local vars
4. injected vars

Because local and injected are merged later, they override earlier names on collisions.

4. Merging and Replacing

merge(view, namedtuple) (src/GeneratedCode/SubContextView.jl) maps return names back to concrete target subcontexts and variables.

• Existing mapped variable: update that mapped target.
• Unknown variable: added to the current local subcontext.

replace(view, (;SubKey => nt)) replaces the full subcontext and is used during init.

merge_into_subcontexts (src/Context/ProcessContexts.jl) enforces that subcontext structure remains valid.

A type-change guard in generated merge asserts the new ProcessContext type stays identical, preventing accidental type instability.