Fwd: Valid java 5 code refuses to compile with lambda-8-b81-linux-x64-12_mar_2013

[Grégoire Neuville]

Yes, I noticed that (lb.<C>apply(map(f)) also works).
 But with a jdk 7 or former, you don't need to explicitly type the
expression for it to compile.
Looks like a bug or a regression to me : jdk1.8 was intended to provide a
(far) better type inference. That's clearly not the case here...


On 17 March 2013 20:14, Sam Pullara <sam at sampullara.com> wrote:

> Looks like the confusion is in type inference. If you have an explicit
> type it does work:
>
>         <B, C> List<C> bind(final List<B> lb, final Func<A, Func<B, C>> f)
> {
>             List<Func<B, C>> map = map(f);
>             return lb.apply(map);
>         }
>
> Sam
>
> On Sat, Mar 16, 2013 at 4:17 PM, Grégoire Neuville
> <gregoire.neuville at gmail.com> wrote:
> > Hello,
> >
> > First of all, let me thank and congratulate you for the hard work you're
> > putting into adding a functional tone to java : this is a great move that
> > will undoubtedly prove itself immensely beneficial.
> >
> > That being said, I'm having a hard time compiling some basic java 5 code
> > with the binary pre-release of both the bare jdk 1.8 and the
> > lambda-enriched one. Indeed, trying to compile the below code :
> >
> > <code>
> >
> >  public class TestJ8 {
> >
> >     interface Func<A, B> {
> >         B f(A a);
> >     }
> >
> >     class List<A> {
> >
> >         <B> List<B> map(Func<A, B> f) {
> >             return null;
> >         }
> >
> >         <B> List<B> bind(Func<A, List<B>> f) {
> >             return null;
> >         }
> >
> >         <B> List<B> apply(final List<Func<A, B>> lf) {
> >             return lf.bind(this::map);
> >         }
> >
> >         <B, C> List<C> bind(final List<B> lb, final Func<A, Func<B, C>>
> f) {
> >             return lb.apply(map(f)); // fails to compile
> >         }
> >
> >     }
> >
> > }
> >
> > </code>
> >
> > fails with the given message :  error: method apply in class
> TestJ8.List<A>
> > cannot be applied to given types
> >
> > Is it expected behaviour or am I missing something (installation steps or
> > whatever...) ?
> >
> > Note : The compiler is invoked through maven with the following
> > configuration :
> >
> > <plugin>
> >             <groupId>org.apache.maven.plugins</groupId>
> >             <artifactId>maven-compiler-plugin</artifactId>
> >             <version>3.0</version>
> >             <configuration>
> >                 <verbose>true</verbose>
> >                 <fork>true</fork>
> >                 <executable>/usr/lib/jvm/java8/bin/javac</executable>
> >                 <compilerArgument>-g</compilerArgument>
> >                 <compilerVersion>1.8</compilerVersion>
> >                 <source>1.8</source>
> >                 <target>1.8</target>
> >             </configuration>
> > </plugin>
> >
> > Thanks !
> >
> > --
> > Grégoire Neuville
> >
>



-- 
Grégoire Neuville



-- 
Grégoire Neuville