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Re: Proposal
- From: Jean-Marie Dautelle <
>
- To:
- Subject: Re: Proposal
- Date: Sun, 2 Nov 2014 11:11:30 +0100
Erratum:
/ Unit-API
interface QuantityFactory {
Length lengthOf(Number, Unit<Length>);
Mass massOf(Number, Unit<Length>);
...
}
On Sun, Nov 2, 2014 at 10:50 AM, Jean-Marie Dautelle
<
>
wrote:
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Hello all,
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I understand your points, but I have the feeling that we are making things
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more difficult than they need to be.
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We should not forget that the main subject is the unit-api not the
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"quantity-api".
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Let's put ourselves in the shoes of the user and see what he might want to
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do:
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public void wait(Time delay) { ... }
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Mass m = parcel.getWeight();
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I would assume that until that point everyone agree... [?]
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Let's go deeper, we might want to do also:
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Length x = ...
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Time t = ...
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Velocity v = x.divide(t);
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If we can do that then I believe that even more people will be happy
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(especially if it does not involve reflection) [?]
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... And YES, it is possible!
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The first thing we see is that some of the quantities interfaces will have
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extra methods.
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interface Length extends Quantity<Length> {
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Area multiply(Quantity<Length>); // Overloading.
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}
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interface Area extends Quantity<Area> {
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Volume multiply(Quantity<Length>); // Overloading.
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}
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Length x = ...
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Volume v = x.multiply(x).multiply(x);
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There is no combination explosion since the number of predefined
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quantities is bounded. Furthermore, all these are convenient (optional)
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methods, the asType(Class<Q>) method can be used for complex cases.
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The question now is how do we create these Quantity instances?
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For this problem, the abstract factory pattern (GoF) is a perfect fit. All
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quantities coming from the same factory will work well together and this
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approach allows for many many optimizations under the hood !
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// Unit-API
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interface QuantityFactory {
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Length lengthOf(double, Unit<Length>);
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Mass massOf(double, Unit<Length>);
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...
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}
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// Unit RI
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abstract class Quantities {
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public static QuantityFactory DOUBLE = ...;
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public static QuantityFactory BIG_DECIMAL = ...;
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}
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Length x = DOUBLE.lengthOf(2.4, METER);
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Length two_x = x.add(x);
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Area x_square = x.multiply(x);
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(Note: I would have preferred plus, minus, time, divide but I can live
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with that [?])
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There is no need for a Measurement class (and MeasurementConverter).
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The quantity base class will be very close to what we have now except it
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does not implement any interface.
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public interface Quantity<Q extends Quantity> {
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Unit<Q> unit();
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Number value();
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double doubleValue(Unit<Q>); // To avoid boxing/deboxing.
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Quantity<Q> add(Quantity<Q>);
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...
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}
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Of course if we can converge on this solution I would be really really
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happy (JScience has many types of numbers such as Rational, Complex for
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which this approach is a perfect fit) !!!
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Best regards,
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Jean-Marie.
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--
It is not the strongest of the species that survives, nor the most
intelligent. It is the one that is most adaptable to change. - Darwin's
Origin of Species (digest)
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