Connection payload/meta

Update Connection to { from addr, to map[addr]payload } where payload describes how connector should interpret incoming message before sending it to receiver.

Payload could be something like:

{
  type: PayloadType # normal | struct field reading
  structField: []string
}

Pros:

• Compile time safety - structure of message is known before program is running so solution this problem must be part of the program itself, like expression in the tree-based languages
• Allows to execute nested access requests like x.y.z in a row without using lots of components and without making the program flow complicated with error checks

Cons

• Leads to modifications of port-address - Must be VERY good thought

Maybe solution for #37

UPD

    net:
      in:
        <name>:
          - nodeType: worker
            name: <worker_name>
            meta:
                connectionType: normal | structReading
                structPath: [foo, bar] # value.foo.bar

from neva.

Component based approach

Use some generic struct field reader component with in: struct, field and out: field

Problems

• Type-checking: since there is no IIP-only ports (ports that are feeded by only const nodes) there is no way to compile-time check if struct has some field or not
  • some err port must be introduces which is bad - in Go we have compile time checks for this set of errors

from neva.

Effect fieldReaders

        nodes:
            fieldReaders:
                userAge:
                    field: age # must throw compile err if needed

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#31 (comment) Choosed

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