Appreciate the feedback. That's a great point. I missed the potential of
the andThen(...) method.
One minor thing to point out - My proposed purpose of the default value
parameter was not to substitute the final value if it is null, but to
substitute the final value if it cannot be obtained, due the *parent* being
null. So in my example, it is the return value of getChild() that would be
null, and your code would fail with a NPE. To handle this using the
chaining approach I think would look something like:
function(ParentBean::getChild)
.andThen(Optional::ofNullable)
.andThen(o -> {
return o.map(ChildBean::getName).orElse("defaultName");
});
So overall it's similar to yours, you just need the .map() call to change
the optional type to match the final return type.
That probably covers a lot of scenarios, however I still consider it a bit
tedious, and it becomes even more tedious if we nest it one level further
because the handling of null is now always an inline function. (I realize
that level of nesting might be rare. I personally have needed it, but I
understand that alone is not justification enough)
For my usage of it, It's still much clearer to see a util method call, with
method references, rather than chaining via andThen, because most uses need
to handle null, which means I'd still be stuck with inline functions
everywhere. In the end the biggest benefit of the util call is the clarity
of quickly knowing that the purpose is to retrieve a simple nested
property, which I don't think you can realistically get when having to
decipher a chain of functions and optionals.
Dan
On Fri, Aug 4, 2023 at 2:04 PM Rob Spoor <apa...@icemanx.nl> wrote:
> With just one simple utility method you can get all the chaining you want:
>
> public static <T, R> Function<T, R> function(Function<T, R> func) {
> return func;
> }
>
> This doesn't look very useful, but it allows you to turn a method
> reference or lambda into a typed Function without needing a cast. After
> that it's really simple using what's provided in the Java API:
>
> Function<MyBean, String> func = function(MyBean::getChild)
> .andThen(Child::getName);
>
> You want a default value? Almost just as easy:
>
> someFrameworkThing.setProperty(function(ParentBean::getChild)
> .andThen(ChildBean::getName)
> .andThen(Optional::ofNullable)
> .andThen(o -> o.orElse("defaultName"));
>
>
> On 04/08/2023 16:04, Daniel Watson wrote:
> > Asking for comments and thoughts on a potential new feature. Already
> > developed in a commons-like style, but dont want to submit PR without
> > discussion as it may be considered out of scope or too use case specific.
> >
> > Justification and details...
> >
> > I've run into a scenario a few times where nested lamba functions would
> be
> > incredibly useful. e.g.
> >
> > MyBean::getChild::getName
> >
> > Obviously this is not a language feature, but can be simulated in a
> useful
> > way. So far my use has mostly been related to code that works with POJO
> > beans, and frameworks that use function references to understand those
> > beans and properties. Specifically useful where the context of the code
> > block is the parent entity, but you need to reference a child, and
> without
> > nested lambdas you end up with things like the below...
> >
> > ParentBean parentBean = new ParentBean();
> > parentBean.setChild(new ChildBean("name"));
> > //imagine that FrameworkThing is a generic class, and thus the generic
> type
> > is ParentBean
> > FrameworkThing someFrameworkThing = new FrameworkThing (ParentBean.class)
> > //but we need to get to a property of a child bean
> > someFrameworkThing.setProperty((parentBean) -> {
> >
> > return parentBean.getChild().getName();
> >
> > });
> >
> > Obviously this could be handled with a getChildName() method on the
> parent
> > bean, but that has pitfalls as well (e.g. bean class cannot be changed,
> or
> > adding of properties interferes with other usage of the class e.g. JPA,
> > JAX). However with a util class the second call can be reduced to
> > something like below, leaving the bean API untouched.
> >
> >
> someFrameworkThing.setProperty(FunctionUtils.nested(ParentBean::getChild,ChildBean::getName));
> >
> > Taken alone, that single reduction may seem trivial, but in a scenario
> > where these nested references are commonly needed, the reduction makes
> the
> > code clearer (In my opinion), as it is immediately apparent on a single
> > line of code that the reference is a simple nested property, rather than
> > having to interpret an inline lambda function. It also discourages errant
> > placement of code by avoiding the inline function (since the only purpose
> > of the lambda was to retrieve a single nested value). In addition, If
> > intermediate nulls need to be handled then the reduction becomes more
> > apparent, as the null checks can be handled in the util class rather than
> > cluttering the app code. e.g.
> >
> >
> someFrameworkThing.setProperty(FunctionUtils.nested(ParentBean::getChild,ChildBean::getName,"defaultName"));
> > //or...
> >
> someFrameworkThing.setProperty(FunctionUtils.nested(ParentBean::getChild,ChildBean::getName,null));
> >
> > The third parameter here is a String (typed genetically based on the
> return
> > type of getName) and indicates the default value to be returned if the
> > first call to getChild() returns null. e.g. it replaces something like...
> >
> > someFrameworkThing.setProperty((parentBean) -> {
> >
> > ChildBean cb = parentBean.getChild();
> > if(cb == null) return null; //or other default value
> > else return cb.getName();
> >
> > });
> >
> > Given that commons-lang aims to extend existing language features, this
> > seemed like a reasonable place for a nested lambda util class. So far my
> > concerns are...
> >
> > 1. Does this feel too specific to an application to warrant
> inclusion in
> > commons? (For me it has been useful enough to place into a common
> library,
> > but commons-lang has a broader scope)
> > 2. If not commons-lang, is there some other commons library that
> this is
> > more suited to?
> > 3. There are still wrinkles that may prove complex and potentially
> > overly specific e.g. exception handling. Does that potential
> complexity
> > make it not worth adding?
> > 4. Assuming the features discussed here *are* valuable, Is handling
> only
> > java.util.Function a complete-enough feature? Or is it useless
> unless it
> > also attempts to handle BiFunctions - which become increasingly
> complex
> > (potentially unfeasible) to implement - i.e. is it too big a feature
> to
> > consider including?
> >
> > If folks feel like this is a solid "no" let me know. If the devil is in
> the
> > details and we need to see the PR first I can do that as well.
> >
> > Dan
> >
>
>
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