Context

Context is a list of mirrors applicable within current method call stack. It contains mirrors of all Elements which are on method call stack.

General Context

Context levels form chains:



Shadows - history of mirrors applied to original ElementPure. When Element is returned to upper Context, it can be Context where its ElementPure original reference was mirrored (possibly subsequently). Then its ElementPure counterpart is resolved back to former reference.

Length of following Shadows chain is independent from length of Context chain. That's because:
  1. only some of the Context nodes in current Context chain have mirrors applicable to given reference
  2. in one ElementPure.original mutation chain there can be several ElementPure nodes, and their mirrors apply to given reference
  3. even one ElementPure mutation generation can have several mirrors which apply in cascade to one object
Shadows.called nodes are a subset of Context.called nodes which had at least one mirror applicable to given reference.




Here mutated sweet_Jane, dear_Jack, mum_Laura, daughter_Jane and student_Jack are accessible only in Context of their "owners" Mr_Jack, Ms_Jane (2x) and Mrs_Laura (2x) respectively. That's because whenever these mutated objects are returned from within their "owners" by getXyzExternal(), they are resolved back to their originals.

Talking on the same page:

Mr_Jack.printGirlfriend() ==> "sweet Jane"


Mr_Jack
.returnGirlfriend() ==> Ms_Jane
  1. Mr_Jack.girlfriend is  sweet_Jane with history of being Ms_Jane outside Context of Mr_Jack
  2. sweet_Jane is returned
  3. sweet_Jane is converted to caller's Context, and because of its history it is resolved back to Ms_Jane
Mrs_Laura.returnDaughter() ==> Ms_Jane
  1. Mrs_Laura.daughter evaluates to daughter_Jane with history of being Ms_Jane outside Context of Mrs_Laura
  2. daughter_Jane is returned
  3. daughter_Jane is converted to caller's Context, and because of its history it is resolved back to Ms_Jane
Mrs_Laura.printDaughter() ==> "daughter Jane"
 
Mr_Jack.printDaughterOf( Mrs_Laura ) ==> "sweet Jane"
  1. Mr_Jack.printDaughterOf( givenPerson ) calls givenPerson.returnDaughter()
    1. Mrs_Laura.daughter field, although within context of Mrs_Laura, is evaluated to sweet_Jane with history of being Ms_Jane outside Context of Mr_Jack. That's because Mr_Jack's mirror [Ms_Jane ==> sweet_Jane] has priority to Mrs_Laura's mirror [Ms_Jane ==> daughter_Jane]
      • This way references to same objects are consistent in various Contexts. References to Ms_Jane get mirrored to sweet_Jane while within Context of Mr_Jack. It applies to both Elements passed there from upper Context, or retrieved from reference field.
    2. Mrs_Laura.returnDaughter() returns sweet_Jane from Context of Mrs_Laura (within Context of Mr_Jack) upwards to Context of Mr_Jack. It's not resolved back to Ms_Jane, because it still remains within Context of Mr_Jack, where it was mirrored to sweet_Jane.
  2. Mr_Jack prints "sweet Jane"
Mr_Jack.returnDaughterOf( Mrs_Laura ) ==> Ms_Jane
  1. Mr_Jack.returnDaughterOf( givenPerson ) calls givenPerson.returnDaughter()
  2. Mrs_Laura.daughter within context of Mr_Jack evaluates to sweet_Jane with history of being Ms_Jane outside Context of Mr_Jack
  3. Mrs_Laura.getDaughter() returns sweet_Jane
  4. Mr_Jack returns sweet_Jane
  5. sweet_Jane is converted to caller's Context, and because of its history it is resolved back to Ms_Jane
These examples show how references are returned from within a Context where they are mirrored. They are resolved to originals from which they were mirrored in actual Context. That's necessary for consistent structural relations in any Context.

@TODO example with a relation in upper Context, mirror in lower Context


Element comparison

There are special situations where inner representation is to be used outside its Context - in methods such as equals(), compareTo(), hashCode(), toString().

Linked chains

 - LIFO use - Shadows
linked upside-down trees - used as maps, e.g. ElementPure's/Context's mirrors
    cascades lists with shared nodes - i.e. trees used upside down
SourceForge.net Logo Copyright (c) 2005, 2006, 2007 Peter Kehl