[jira] [Commented] (GROOVY-8255) Odd problems with flow typing and generics in Groovy 2.4.12+

["Paul King (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-8255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16178199#comment-16178199 ] 

Paul King commented on GROOVY-8255:
-----------------------------------

Standalone example:
{code}
@groovy.transform.CompileStatic
class Foo {
    List<List<String>> items = [['x']]
    def bar() {
        def result = []
        List<String> selections = items.get(0) ?: [] // ['y'] okay
        for (String selection: selections) {
            result << selection
        }
        result
    }
}

assert new Foo().bar() == ['x']
// [Static type checking] - Incompatible generic argument types.
// Cannot assign java.util.List <? extends java.lang.Object>
// to: java.util.List <String>
{code}

> Odd problems with flow typing and generics in Groovy 2.4.12+
> ------------------------------------------------------------
>
>                 Key: GROOVY-8255
>                 URL: https://issues.apache.org/jira/browse/GROOVY-8255
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static Type Checker
>    Affects Versions: 2.4.12
>            Reporter: Graeme Rocher
>
> In order to get the GORM codebase to compile I had to make this change:
> https://github.com/grails/grails-data-mapping/commit/1ef850c496d13d8ca915b27e76b6bfdb4e27377e
> The code in question is:
> {code}
>     /**
>      * Sets multipart values within the request body
>      *
>      * @param name The name of the multipart
>      * @param value The value of the multipart
>      */
>     void setProperty(String name, value) {
>         if (value instanceof File) {
>             value = new FileSystemResource(value)
>         }
>         else if (value instanceof URL) {
>             value = new UrlResource(value)
>         }
>         else if (value instanceof InputStream) {
>             value = new InputStreamResource(value)
>         }
>         else if (value instanceof GString) {
>             value = value.toString()
>         }
>         if( mvm[name] ) {
>             mvm[name].add value    
>         }
>         else {
>             mvm.put(name, [value]) // <--- FAILS COMPILATION HERE
>         }        
>     }
> {code}
> No matter what I tried I could not get it into to compile. The method accepts `put(String, List<Object>)` but fails compilation with:
> {code}
> RequestCustomizer.groovy: 392: [Static type checking] - Cannot call org.springframework.util.MultiValueMap <String, Object>#put(java.lang.String, java.lang.Object) with arguments [java.lang.String, java.util.List <java.lang.String>] 
>  @ line 392, column 13.
>                mvm.put(name, [value])
>                ^
> {code}
> Altering the code to:
> {code}
>        List<Object> values = [value]
>        mvm.put(name, values)
> {code}
> Fails with:
> {code}
> RequestCustomizer.groovy: 392: [Static type checking] - Incompatible generic argument types. Cannot assign java.util.List <java.lang.String> to: java.util.List <Object>
>  @ line 392, column 35.
>                List<Object> values = [value]
>                                      ^
> RequestCustomizer.groovy: 393: [Static type checking] - Cannot call org.springframework.util.MultiValueMap <String, Object>#put(java.lang.String, java.lang.Object) with arguments [java.lang.String, java.util.List <java.lang.String>] 
>  @ line 393, column 13.
>                mvm.put(name, values)
>                ^
> 2 errors
> {code}



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