[Enh]: MAMessagingStringWriter

Enables delegating string writing to an arbitrary object via any of its messages. 

*Limitation:* cannot be used when 1) the message receiver is the container and 2) descriptions are cached e.g. when using the description for the first object in a homogeneous collection for the whole collection.

Here is an example (which illustrates #1 in the limitation above and so wouldn't work with a cached description):

```
MyDomainClass>>employeeDescription
	<magritteDescription>
	
	| message writer reference |
	message := MessageSend 
		receiver: self
		selector: #employeeDisplayString.
	
	writer := MAMessagingStringWriter new
		messageSend: message.
	
	reference := MAContainer new 
		stringWriter: writer;
		yourself.

	^ MAToOneRelationDescription new
		reference: reference;
		accessor: #employee;
		yourself
```

source/Magritte-Model/MAMessagingStringWriter.class.st

@@ -0,0 +1,66 @@
+"
+I enable delegating string writing to an arbitrary object via any of its messages. 
+
+*Limitation:* I cannot be used when 1) the message receiver is the container and 2) descriptions are cached e.g. when using the description for the first object in a homogeneous collection for the whole collection.
+
+Here is an example (which illustrates #1 in the limitation above and so wouldn't work with a cached description):
+
+```
+MyDomainClass>>employeeDescription
+	<magritteDescription>
+	
+	| message writer reference |
+	message := MessageSend 
+		receiver: self
+		selector: #employeeDisplayString.
+	
+	writer := MAMessagingStringWriter new
+		messageSend: message.
+	
+	reference := MAContainer new 
+		stringWriter: writer;
+		yourself.
+
+	^ MAToOneRelationDescription new
+		reference: reference;
+		accessor: #employee;
+		yourself
+```
+"
+Class {
+	#name : #MAMessagingStringWriter,
+	#superclass : #MAStringWriter,
+	#instVars : [
+		'messageSend'
+	],
+	#category : #'Magritte-Model-Visitor'
+}
+
+{ #category : #accessing }
+MAMessagingStringWriter >> messageSend [
+	^ messageSend
+]
+
+{ #category : #accessing }
+MAMessagingStringWriter >> messageSend: anObject [
+	Halt if: [ anObject receiver employee isNil ].
+	messageSend := anObject
+]
+
+{ #category : #accessing }
+MAMessagingStringWriter >> visitContainer: aDescription [
+
+	self visitDescription: aDescription
+]
+
+{ #category : #'as yet unclassified' }
+MAMessagingStringWriter >> visitDescription: aDescription [
+
+	self stream nextPutAll: self messageSend value
+]
+
+{ #category : #'as yet unclassified' }
+MAMessagingStringWriter >> visitElementDescription: aDescription [
+
+	self visitDescription: aDescription
+]