Change the way an Object is printed - Revision history

Nmingott at 23:09, 4 May 2025

2025-05-04T23:09:00Z

← Older revision		Revision as of 23:09, 4 May 2025
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	'''Problem'''. Suppose you defined a Class, say '''User''', and suppose this class contains the instance variables <code>name</code>, <code>id</code>, <code>password</code>. When you create a new User object, it will print itself as <code>aUser</code>. This might be ok, but suppose it is usefull for you to always see <code>id</code>. What to do?		'''Problem'''. Suppose you defined a Class, say '''User''', and suppose this class contains the instance variables <code>name</code>, <code>id</code>, <code>password</code>. When you create a new User object, it will print itself as <code>aUser</code>. This might be ok, but suppose it is usefull for you to always see <code>id</code>. What to do?

	'''Solution'''. In the User object define the method <code>printOn:</code>. Watch how it is defined on the class <code>Object</code> and change it a bit, for example as:		'''Solution'''. In the User object define the method <code>printOn:</code>. Watch how it is defined on the class <code>Object</code> and change it a bit, for example as:<syntaxhighlight lang="smalltalk">
	printOn: aStream		printOn: aStream
	\|str\|		\|str\|
	str := ((self class name withArticle) , '-', self id asString).		str := ((self class name withArticle) , '-', self id asString).
	aStream nextPutAll: str.		aStream nextPutAll: str.
	Cy. Defect: The method above is a bit Pythonic.		</syntaxhighlight>Cy. Defect: The method above is a bit Pythonic.

	This method definition is more Smalltalkish:		This method definition is more Smalltalkish:<syntaxhighlight lang="smalltalk">
	printOn: aStream		printOn: aStream
	aStream		aStream nextPutAll: self class name;
	~~nextPutAll:~~ ~~self~~ ~~class~~ ~~name~~;		nextPut: $-;
	~~nextPut~~: ~~$-;~~		nextPutAll: self id asString .
		⚫	</syntaxhighlight>Voila, now if you print a user you will see something like <code>aUser-2132</code>. This very practical when you are listing several user objects, for the example in the inspector.
	nextPutAll: self id asString
⚫	Voila, now if you print a user you will see something like <code>aUser-2132</code>. This very practical when you are listing several user objects, for the example in the inspector.
	----NM 10-Aug-2021. Tested Cuis5.0-4738.image		----NM 10-Aug-2021. Tested Cuis5.0-4738.image

Nmingott: imported material

2025-05-03T23:24:04Z

imported material

← Older revision		Revision as of 23:24, 3 May 2025
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	'''Solution'''. In the User object define the method <code>printOn:</code>. Watch how it is defined on the class <code>Object</code> and change it a bit, for example as:		'''Solution'''. In the User object define the method <code>printOn:</code>. Watch how it is defined on the class <code>Object</code> and change it a bit, for example as:
	printOn: aStream		printOn: aStream
	\|str\|		\|str\|
	str _ ((self class name withArticle) , '-', self id asString).		str := ((self class name withArticle) , '-', self id asString).
	aStream nextPutAll: str.		aStream nextPutAll: str.
	Cy. Defect: The method above is a bit Pythonic.		Cy. Defect: The method above is a bit Pythonic.

	This method definition is more Smalltalkish:		This method definition is more Smalltalkish:
	printOn: aStream		printOn: aStream
	aStream		aStream
	nextPutAll: self class name;		nextPutAll: self class name;
	nextPut: $-;		nextPut: $-;
	nextPutAll: self id asString		nextPutAll: self id asString
	Voila, now if you print a user you will see something like <code>aUser-2132</code>. This very practical when you are listing several user objects, for the example in the inspector.		Voila, now if you print a user you will see something like <code>aUser-2132</code>. This very practical when you are listing several user objects, for the example in the inspector.
	----NM 10-Aug-2021. Tested Cuis5.0-4738.image		----NM 10-Aug-2021. Tested Cuis5.0-4738.image

Nmingott: imported material

2025-05-03T23:22:56Z

imported material

New page

'''Problem'''. Suppose you defined a Class, say '''User''', and suppose this class contains the instance variables <code>name</code>, <code>id</code>, <code>password</code>. When you create a new User object, it will print itself as <code>aUser</code>. This might be ok, but suppose it is usefull for you to always see <code>id</code>. What to do?

'''Solution'''. In the User object define the method <code>printOn:</code>. Watch how it is defined on the class <code>Object</code> and change it a bit, for example as:
printOn: aStream
|str|
str _ ((self class name withArticle) , '-', self id asString).
aStream nextPutAll: str.
Cy. Defect: The method above is a bit Pythonic.

This method definition is more Smalltalkish:
printOn: aStream
aStream
nextPutAll: self class name;
nextPut: $-;
nextPutAll: self id asString
Voila, now if you print a user you will see something like <code>aUser-2132</code>. This very practical when you are listing several user objects, for the example in the inspector.
----NM 10-Aug-2021. Tested Cuis5.0-4738.image