Morphic

Morphic is the parent class of ProxyService and delegates its identity to its defaultHandler class. A Morphic class object can thus change its state and behavior at runtime by changing the defaultHandler. But Proteus makes use of this class through its ProxyService class.

The Morphic class inherits from PreinitObject, and directly defines only those properties necessary to concatenate its ‘self’ identity with that of its defaultHandler, a construct() method to initialize its vocabulary and containment relationships, a defaultHandler property, and a propNotDefined() method to capture all other messages and delegate them to its defaultHandler object.

In addition, the proteus.h header defines templates for Morphic similar to those provided for Thing, to facilitate shortcut vocabulary, description, and location properties.

Suppose we want to make a bowl of class Container. We could use the usual definition:

bowl: Container

{

‘bowl’ ‘bowl’ @livingRoom

}

This object inherits its states and behaviors from Container class. We can examine the definition returned by the @show metacommand:

Object staticBowl extends Container

{

DynamOrAnon: nil UnnamedInternal: nil Transient: nil

properties directly defined by object staticBowl

vocabWords_ : TypeSString = 'static bowl'

location : TypeObject = livingRoom

name : TypeSString = 'static bowl'

adjective : TypeList = ['static']

noun : TypeList = ['bowl']

objRefTag : TypeSString = 'tads#55c'

tmpAmbient_ : TypeInt = 0

tmpAmbientWithin_ : TypeInt = 0

tmpAmbientFill_ : TypeNil = nil

tmpTrans_ : TypeEnum = transparent

tmpTransWithin_ : TypeEnum = opaque

tmpObstructor_ : TypeNil = nil

tmpObstructorWithin_ : TypeNil = nil

tmpFillMedium_ : TypeNil = nil

explicitVisualSenseInfo : TypeNil = nil

}

Alternatively, we could define our bowl using the Morphic class, as follows:

bowl: Morphic

{

'bowl' 'bowl' @livingRoom

defaultHandler = Container

}

Let’s examine the Morphic bowl using the @show command:

Object morphicBowl extends Morphic, tads#64f (Container)

{

DynamOrAnon: nil UnnamedInternal: nil Transient: nil

properties directly defined by object morphicBowl

vocabWords_ : TypeSString = 'morphic bowl'

location : TypeObject = livingRoom

name : TypeSString = 'morphic bowl'

defaultHandler : TypeObject = tads#64f (Container)

isDoingExec_ : TypeNil = nil

isExecuted_ : TypeTrue = true

objRefTag : TypeSString = 'tads#577'

adjective : TypeList = ['morphic']

noun : TypeList = ['bowl']

tmpAmbient_ : TypeInt = 0

tmpAmbientWithin_ : TypeInt = 0

tmpAmbientFill_ : TypeNil = nil

tmpTrans_ : TypeEnum = transparent

tmpTransWithin_ : TypeEnum = opaque

tmpObstructor_ : TypeNil = nil

tmpObstructorWithin_ : TypeNil = nil

tmpFillMedium_ : TypeNil = nil

explicitVisualSenseInfo : TypeNil = nil

}

From this we can see that the Morphic bowl defines a few extra properties: &isDoingExec_ and &isExecuted_. These belong to the PreinitObject class and were generated when the object was constructed.

But notice that the Morphic bowl extends an instance of Container, rather than Container class itself. The reason for this is to perform a subtle piece of trickery with the propDefined() method. Consider the following:

propDefined(&isOpen)	morphicBowl	staticBowl
PropDefAny	true	true
PropDefDirectly	nil	nil
PropDefInherits	true	true
PropDefGetClass	Container	Container

By delegating to an instance of the handler class, instead of the class itself we maintain the same relationships of the propDefined() intrinsic method for morphicBowl as for staticBowl. It also allows getPropList() and getPropParams() to remain consistent with that of staticBowl.

The states and behaviors of the object are roughly the same as though it inherited from Container, but it still has some differences, due to the structures of their inheritance trees.

But the biggest difference is that the Morphic object can change its class structure during runtime. For instance, suppose we want the bowl to change from Container to Surface class when something is put into it. We can code this as follows:

morphicBowl: Morphic

{

'morphic bowl' 'morphic bowl' @livingRoom

defaultHandler = Container

iobjFor(PutIn)

{

action()

{

delegated (getHandler())();

setHandler(Surface);

}

Notice that we can’t use the inherited() keyword to pass control down the inheritance tree, we must use the delegated() keyword (the same command that is used by propNotDefined()). Now when an object is put into the bowl it is converted into a Surface. Examining the object definition with the @show metacommand gives us the following:

Object morphicBowl extends Morphic, tads#6bd (Surface)

{

DynamOrAnon: nil UnnamedInternal: nil Transient: nil

properties directly defined by object morphicBowl

vocabWords_ : TypeSString = 'morphic bowl'

location : TypeObject = livingRoom

name : TypeSString = 'morphic bowl'

actionIobjPutIn(0, 0, nil) : TypeCode

defaultHandler : TypeObject = tads#6bd (Surface)

isDoingExec_ : TypeNil = nil

isExecuted_ : TypeTrue = true

objRefTag : TypeSString = 'tads#577'

adjective : TypeList = ['morphic']

noun : TypeList = ['bowl']

tmpAmbient_ : TypeInt = 0

tmpAmbientWithin_ : TypeInt = 0

tmpAmbientFill_ : TypeNil = nil

tmpTrans_ : TypeEnum = transparent

tmpTransWithin_ : TypeEnum = opaque

tmpObstructor_ : TypeNil = nil

tmpObstructorWithin_ : TypeNil = nil

tmpFillMedium_ : TypeNil = nil

explicitVisualSenseInfo : TypeNil = nil

contents : TypeList = [brassKey]

described : TypeTrue = true

}

And now the command <<examine bowl>> produces the following display:

>x morphic bowl

On the morphic bowl is a brass key.

Of course we would probably want to change the vocabulary and name of the bowl to represent its new structure.

This file is part of the TADS 3 Proteus Library Extension