This class provides an abstract base for all structures that can be used by external functions. ExternalStructures have two possible handle types:
- ExternalAddress
If the handle is an external address then the object described does not reside in the Smalltalk object memory.
- ByteArray
If the handle is a byte array then the object described resides in Smalltalk memory.
Useful methods should be implemented by subclasses of ExternalStructure using the common ByteArray/ExternalAddress platform dependent access protocol which will transparently access the correct memory location.

	inspecting
	inspect

	printing
	longPrintOn:

	converting
	externalType

	field definition
	byteSize compileAlias:withAccessors: compileAllFields compileFields compileFields: compileFields:withAccessors: compiledSpec defineAliasAccessorsFor:type: defineFieldAccessorsFor:startingAt:type: defineFields defineFields: fields

	instance creation
	externalNew fromHandle: new

	initialize-release	top
	free Free the handle pointed to by the receiver

	inspecting	top
	inspect Open an ExternalStructureInspector on the receiver. Use basicInspect to get a normal (less useful) type of inspector.

	printing	top
	longPrintOn: Append to the argument, aStream, the names and values of all the record's variables.

	class management	top
	doneCompiling I have been recompiled. Update any types that reference me.
	fileOutInitializerOn:
	fileOutOn:moveSource:toFile:initializing: File a description of the receiver on aFileStream. If the boolean argument, moveSource, is true, then set the trailing bytes to the position of aFileStream and to fileIndex in order to indicate where to find the source code.
	obsolete The receiver is becoming obsolete. NOTE: You if you remove the whole class category at once, you cannot assume that the ExternalType class is still present.
	rename: The new name of the receiver is the argument, aString.

	converting	top
	externalType Return an external type describing the receiver as a structure

	field definition	top
	byteSize Return the size in bytes of this structure.
	compileAlias:withAccessors: Define all the fields in the receiver. Return the newly compiled spec.
	compileAllFields ExternalStructure compileAllFields
	compileFields Compile the field definition of the receiver. Return the newly compiled spec.
	compileFields: Compile the field definition of the receiver. Return the newly compiled spec.
	compileFields:withAccessors: Define all the fields in the receiver. Return the newly compiled spec.
	compiledSpec Return the compiled spec of the receiver
	defineAliasAccessorsFor:type: Define read/write accessors for the given field
	defineFieldAccessorsFor:startingAt:type: Define read/write accessors for the given field
	defineFields Define all the fields in the receiver
	defineFields: Define all the fields in the receiver
	fields Return the fields defining the receiver

	instance creation	top
	externalNew Create an instance of the receiver on the external heap
	fromHandle:
	new Answer a new instance of the receiver (which is a class) with no indexable variables. Fail if the class is indexable.