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https://issues.apache.org/jira/browse/SIS-578?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Martin Desruisseaux closed SIS-578.
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> Remove contravariance in filters and expressions
> ------------------------------------------------
>
> Key: SIS-578
> URL: https://issues.apache.org/jira/browse/SIS-578
> Project: Spatial Information Systems
> Issue Type: Task
> Components: Features
> Affects Versions: 1.1, 1.2, 1.3
> Reporter: Martin Desruisseaux
> Assignee: Martin Desruisseaux
> Priority: Major
> Fix For: 1.4
>
>
> Since SIS 1.1, Filters and expressions in {{org.apache.sis.filter}} package
> have methods with a signature like below. This signature reproduced the state
> of GeoAPI 3.1 draft (not yet released).
> {code:java}
> List<Expression<? super R, ?>> getParameters();
> {code}
> However experience has shown that contravariance (the {{<? super>}} part)
> cause difficulties that are hard to resolve. The problem is that filters are
> often chained. When a code follows a chain of filters, it may need to check
> for parameters of parameters. In such cases, invoking the above
> {{getParameters()}} method, then invoking again {{getParameters()}} on the
> result, gives a type that looks like {{<? super ? super R>>, which is
> identified by the Java compiler as {{<? super #CAP1>}}. The consequence is
> many compilation errors of the kind "no method match {{List<Expression<?
> super #CAP1, ?>>}} which are hard to resolve otherwise than by unsafe cast.
> Consequently, for having more type-safe code, it seems necessary to change
> above method signature like below:
> {code:java}
> List<Expression<R, ?>> getParameters();
> {code}
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