Displaying the Structure of an Object

An author might want to display the structural details of an object or the comparison of two objects. Proteus provides a set of messages that can be used for this purpose.

The displayStructure([cond]) Message

Everything from the previous chapters comes together in this message. We display the structure of the object in a format that mirrors its source definition.

The message takes a variable argument list cond which, if present, should be the same as that acceptable to the getStrucList() message.

For instance, the message me.displayStructure() displays something like the following:

Object me extends Person

{

DynamOrAnon: nil UnnamedInternal: nil Transient: nil

Lists: Parents Children First Named Ancestors First Named Descendants

Trees: Ancestors Descendants Containment Modifications

Properties: Defined Action State State Delta

properties directly defined by object me

bulkCapacity : TypeInt = 5

issueCommandsSynchronously : TypeTrue = true

location : TypeObject = livingRoom

nextHoldingIndex : TypeInt = 5

contents : TypeList = [duffel, keyring, trophy, whiteBox]

pendingCommand : TypeObject = Vector []

antecedentTable : TypeObject = LookupTable []

memoryTable : TypeObject = LookupTable [[television, true], [poBox, true], [staticBowl, true], [smallRedBall, true], [redBook, true], [ironKey, true], [clearJar, true], [greenJar, true], [tads#5d5 (CopperCoin), true], [tads#5d6 (CopperCoin), true], [blueBook, true], [brassKey, true], [box, true], [tricycle, true], [rustyKey, true], [greenBall, true], [eightball, true], [bigRedBall, true], [tads#5d7 (SilverCoin), true], [tads#5dc (GoldCoin), true], [tads#5db (GoldCoin), true], [tads#5dd (GoldCoin), true], [tads#5de (GoldCoin), true], [tads#5da (GoldCoin), true], [tads#5d9 (SilverCoin), true], [tads#5d8 (SilverCoin), true], [morphicBowl, true], [bill, true], [bob, true], [livingRoom, true], [trophy, true], [vase, true], [tads#615 (Candle), true], [tads#617 (StretchyContainer), true], [tads#618 (Container), true], [tads#619 (Thing), true], [tads#616 (Odor), true], [diningRoom, true], [duffel, true], [keyring, true], [whiteBox, true], [beeperNoise, true]]

objRefTag : TypeSString = 'tads#588'

tmpAmbient_ : TypeInt = 0

tmpAmbientWithin_ : TypeInt = 0

tmpAmbientFill_ : TypeNil = nil

tmpTrans_ : TypeEnum = transparent

tmpTransWithin_ : TypeEnum = transparent

tmpObstructor_ : TypeNil = nil

tmpObstructorWithin_ : TypeNil = nil

tmpFillMedium_ : TypeNil = nil

scheduleOrder : TypeInt = 100

locationBefore : TypeObject = livingRoom

locationLitBefore : TypeTrue = true

followingActor : TypeNil = nil

moved : TypeTrue = true

lastTravelDest : TypeObject = livingRoom

lastTravelBack : TypeObject = diningRoom

mostRecentAction : TypeObject = tads#6ff (predicate(ListChildObj))

nextRunTime : TypeInt = 4

}

Elements in blue represent hyperlinks that perform various functions.

Object Header

The first part of the display consists of an object header, composed of three parts:

The first part is the keyword Class or Object, which indicates whether the object is a class or more generally an object
The object’s tag and symbol, in this case me
The objects from which this object is extended (referenced by object reference tags and symbols), in this case Actor.

Object Characteristics

The next part of the display consists of a section that further attempts to classify the object, based largely on information obtained from the global symbol table:

isDynamOrAnon() == nil: This is an equality relationship (==) that represents whether the object is dynamically-created/anonymously-defined or not. In the case of me, this is nil.
isUnnamedInternal() == nil: This is an equality relationship (==) that represents whether the object is an unnamed internal – the result of a modification of an object through the modify keyword. In the case of me this is nil.
isTransient ()== nil: This is an equality relationship (==) that represents whether the object is transient or not. This information is available as an object message, but is displayed here for convenience. In the case of me this is nil.

Object Lineage Listings

The next section of the display is a set of hyperlinks that produce unordered lists detailing various aspects of the object’s lineage:

Parents: produces an unordered list of this object’s parents
Children: produces an unordered list of this object’s children
First Named Ancestors: produces an unordered list of this object’s first named ancestors
First Named Descendants: produces a n unordered list of this object’s first named descendants

Object Lineage Trees

One of the most interesting set of hyperlinks consist of the trees of Ancestors, Descendants, Containment, and Modifications. These produce a tree structure of the corresponding relationship of this object to others.

Directly Defined Property List

The next part of the display is divided into sections of directly defined property lists for each object we encounter as we traverse the inheritance hierarchy. The display above is only a partial traversal, caused by the cond argument passed as part of the getStrucList() message.

The directly defined property list has the format:

propertyName: Type <= assignedValue>

The elements of the format are defined below:

propertyName: This is the string representation of the symbolic retrieved for the property. The hyperlink trees the definers of the property
Type: This is the TypeXXXX value returned from the propType() message and indicates the type of the property.
<= assignedValue>: This only applies to object attributes, and is displayed in a format representative of its Type.

So, from our example above me directly defines the property location, which is currently of TypeObject and is assigned the value entryway. The property pendingCommand is currently of TypeObject, and is assigned the value Vector. This is a dynamically-created instance of the class Vector, and we can see from the display that it is empty ([]).

The empty braces after Vector is a special aspect of the display mechanism, and not part of the vector object’s name. For any Collection class object displayStructure() will display it’s elements.

Displaying the State Delta for Two Objects

The message displayStateDelta(otherObj, sup, [bypass]) is similarly used to display the state delta between two objects. The display looks something like the following:

========== START TADS 3 DIAGNOSTIC ==========

State Delta: tads#668 (Person), me

tads#668 (Person).nextHoldingIndex : TypeInt = 3

me.nextHoldingIndex : TypeInt = 39

tads#668 (Person).contents : TypeList = [duffel, keyring]

me.contents : TypeList = [duffel, tads#5de (GoldCoin), tads#5d7 (SilverCoin), tads#5d9 (SilverCoin), tads#5d8 (SilverCoin)]

tads#668 (Person).nextRunTime : TypeInt = 0

me.nextRunTime : TypeInt = 1

tads#668 (Person).mostRecentAction : TypeNil = nil

me.mostRecentAction : TypeObject = tads#64b (predicate(Take))

========== END TADS 3 DIAGNOSTIC ============

The display simply pairs the attributes that are different between the two objects and displays them in a format similar to that of displayStructure().

This file is part of the TADS 3 Proteus Library Extension