On Wed, 7 Aug 2013 18:04:39 -0400, Evan Ward wrote:
Hi,
As a grateful user of the library, I would prefer the Fluent API and
immutability. I have implemented this pattern in some of my own
projects
and it makes the API very easy to use.
Most of the time, when the interface is small, inheritance isn't
really
necessary and I just implement the withXxx methods directly. A one
line
'return new ...' isn't hard to maintain with IDE support for renames
and
add/remove parameters.
When inheritance is part of the API you can parametrize the base
class
and add an abstract create method, like so:
abstract class Parent<T extends Parent> implements Interface{
protected abstract T create(...);
public T withXxx(x){
return create(x, ...);
}
}
class Child extends Parent<Child> {
protected T create(...){
return new Child(...);
}
}
Did I understand correctly that the base class "Parent" is assumed to
have complete knowledge of all its subclass "Child": the signature of
"create" must contain the arguments for fields declared in "Child"?
Gilles
The create method forces the implementing class to have an
appropriate
constructor. The withXxx methods are implemented only once and the
inheriting class only has to implement one more method. The type
parameterization is invisible to the user if they use the Child class
or
the Interface. The down side is that Child can not be subclassed
correctly, but this enforces the rule "design for inheritance or
prevent
it". This is similar to the pattern used in MarkupBuilder from
jatl.[1]
(jatl uses a mutable base class)
Regards,
Evan
[1]
http://code.google.com/p/jatl/source/browse/src/main/java/com/googlecode/jatl/MarkupBuilder.java
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