Contravariance - Revision history

JaroslavTulach at 15:31, 14 July 2016

2016-07-14T15:31:44Z

←Older revision		Revision as of 15:31, 14 July 2016
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	More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]].		More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]].
		+
		+	[[Category:APIDesignPatterns]]
		+	[[Category:APIDesignPatterns:Evolution]]

JaroslavTulach at 09:21, 13 December 2011

2011-12-13T09:21:45Z

←Older revision		Revision as of 09:21, 13 December 2011
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	<source lang="java" snippet="variance.contravariance.v2"/>		<source lang="java" snippet="variance.contravariance.v2"/>

-	Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]] ~~code~~ like ~~following~~ will ~~have problems:~~	+	Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]], we'll have a problem. Code like this will compile fine, but...

	<source lang="java" snippet="variance.contravariance.test"/>		<source lang="java" snippet="variance.contravariance.test"/>

-	If compiled against version 1.0 and executed against version 2.0, it will throw linkage errors:	+	...if compiled against version 1.0 and executed against version 2.0, it will throw linkage errors:

	<source lang="bash">		<source lang="bash">

JaroslavTulach at 17:33, 19 October 2011

2011-10-19T17:33:35Z

←Older revision		Revision as of 17:33, 19 October 2011
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-	Everything one would ever like to know about [[Covariance]] and [[Contravariance]] is available at [[wikipedia:Covariance_and_contravariance_(computer_science)\|wikipedia]]. Here is just a small example how it does not work in [[Java]].	+	Everything one would ever like to know about [[Covariance]] and [[Contravariance]] is available at [[wikipedia:Covariance_and_contravariance_(computer_science)\|wikipedia]]. Here is just a small example how it does not work in [[Java]] (the argumentation is the same as in case of [[Covariance]]). First version would like to be fixed:

-	[[~~TBD~~]]	+	<source lang="java" snippet="variance.contravariance.v1"/>
		+
		+	However when one tries to change the parameter type:
		+
		+	<source lang="java" snippet="variance.contravariance.v2"/>
		+
		+	Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]] code like following will have problems:
		+
		+	<source lang="java" snippet="variance.contravariance.test"/>
		+
		+	If compiled against version 1.0 and executed against version 2.0, it will throw linkage errors:
		+
		+	<source lang="bash">
		+	Mixing should not work: Compiling with version 1.0 and running against version 2.0 fails.
		+	Exception in thread "main" java.lang.NoSuchMethodError: api.Contravariance.isPositive(Ljava/lang/Integer;)Z
		+	at test.ContravarianceTest.main(Unknown Source)
		+	Java Result: 1
		+	</source>
		+
		+	More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]].

JaroslavTulach: New page: Everything one would ever like to know about Covariance and Contravariance is available at wikipedia. Here is just a ...

2011-10-18T05:42:47Z

New page: Everything one would ever like to know about Covariance and Contravariance is available at wikipedia. Here is just a ...

New page

Everything one would ever like to know about [[Covariance]] and [[Contravariance]] is available at [[wikipedia:Covariance_and_contravariance_(computer_science)|wikipedia]]. Here is just a small example how it does not work in [[Java]].

[[TBD]]