Converting between structurally compatible function types

[Samir Talwar]

Java can't, in general, assign a value to another of the same type with
different generic parameters. Just like there's no implicit conversion from
List<String> to List<Object>, you can't convert Function objects either.

My preferred way of doing this would be to use the fact that Function is
really a class with the method `apply` and assign a method reference
instead:

        Function<String, Object> g = f::apply;

Cheers,

— Samir.

On Mon, Feb 23, 2015 at 5:36 PM, Millies, Sebastian <
Sebastian.Millies at softwareag.com> wrote:

> sorry for the noise, figured out how to use the identity function for this:
>
> Function<Integer,Object> id = n -> n
> g = id.compose(f);
>
> -- Sebastian
>
> -----Original Message-----
> From: lambda-dev [mailto:lambda-dev-bounces at openjdk.java.net] On Behalf
> Of Millies, Sebastian
> Sent: Monday, February 23, 2015 6:32 PM
> To: lambda-dev at openjdk.java.net
> Subject: Converting between structurally compatible function types
>
> Hello there,
>
> I have a very basic question: why does the following not compile:
>
> Function<String,Integer> f = s -> 1;
> Function<String,Object> g = f;
>
> After all, I would expect that anywhere where a function from String to
> arbitrary objects is required, I can supply a function to integers in
> particular.
> I guess Java just sees the names are different, and that’s it?
>
> How do I best convert between the two types?
>
>
> n  Sebastian
>
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