[weld-issues] [JBoss JIRA] Commented: (WELDX-188) Provide utility to check if Type is assignable to another Type

[Dan Allen (JIRA)]

    [ https://jira.jboss.org/browse/WELDX-188?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12561670#action_12561670 ] 

Dan Allen commented on WELDX-188:
---------------------------------

Ah, parameters are strictly typed. So while the exact still shouldn't be exact, parameter types do have to be equal.

I'll provide three test cases that should pass.

Type generalType1 = new TypeLiteral<Instance<? extends Number>>() {}.getType();
Type specificType1 = new TypeLiteral<Instance<Integer>>() {}.getType();
Assert.assertTrue(TypeHelper.get(generalType1).isAssignableFrom(specificType1));

Type generalType2 = new TypeLiteral<Provider<? extends Number>>() {}.getType();
Type specificType2 = new TypeLiteral<Instance<Integer>>() {}.getType();
Assert.assertTrue(TypeHelper.get(generalType2).isAssignableFrom(specificType2));

Type generalType3 = new TypeLiteral<Number>() {}.getType();
Type specificType3 = new TypeLiteral<Integer>() {}.getType();
Assert.assertTrue(TypeHelper.get(generalType3).isAssignableFrom(specificType3));

Being able to shove off dealing with the specifics of the various types is quite helpful.


> Provide utility to check if Type is assignable to another Type
> --------------------------------------------------------------
>
>                 Key: WELDX-188
>                 URL: https://jira.jboss.org/browse/WELDX-188
>             Project: Weld Extensions
>          Issue Type: Feature Request
>            Reporter: Dan Allen
>            Priority: Minor
>             Fix For: 1.0.0.Beta2
>
>
> Often times when writing an extension, you need to know if one Type is assignable from another Type. This is a more sophisticated version of Class#isAssignableFrom(Class) which takes into account paramaterized types.
> given
>    parameterized type Bean<N extends Number>
> then
>   type Bean<Number> is assignable from type Bean<Integer>
> One area where this is useful is when checking if a bean type is more specific than another bean type. It's not sufficient to assume the bean type is a simple class.
> Something similar to what is provided by: http://google-gson.googlecode.com/svn-history/r442/trunk/gson/src/main/java/com/google/gson/reflect/TypeToken.java

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