Specification pattern: Difference between revisions

Revision as of 19:45, 14 April 2020

Revision as of 11:52, 25 July 2020

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=== [[C Sharp (programming language)|C#]] ===

<sourcesyntaxhighlight lang="csharp">

public interface ISpecification

{

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}

</syntaxhighlight>

</source>

=== [[C Sharp (programming language)|C# 6.0]] with generics ===

<sourcesyntaxhighlight lang="csharp">

public interface ISpecification<T>

{

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public override bool IsSatisfiedBy(T candidate) => !other.IsSatisfiedBy(candidate);

}

</syntaxhighlight>

</source>

=== [[Python (programming language)|Python]] ===

<sourcesyntaxhighlight lang="python">

from abc import abstractmethod

from dataclasses import dataclass

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return not self.subject.is_satisfied_by(candidate)

</syntaxhighlight>

</source>

==Example of use==

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Using these three specifications, we created a new specification called SendToCollection which will be satisfied when an invoice is overdue, when notices have been sent to the customer, and are not already with the collection agency.

<sourcesyntaxhighlight lang="csharp">

var OverDue = new OverDueSpecification();

var NoticeSent = new NoticeSentSpecification();

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}

}

</syntaxhighlight>

</source>

== Criticisms ==

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Alternative example, without the Specification Pattern:

<sourcesyntaxhighlight lang="csharp">

var InvoiceCollection = Service.GetInvoices();

foreach (var invoice in InvoiceCollection) invoice.SendToCollectionIfNecessary();

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private bool ShouldSendToCollection() => currentInvoice.OverDue && currentInvoice.NoticeSent && !currentInvoice.InCollection;

</syntaxhighlight>

</source>This alternative uses foundation concepts of get-only properties, condition logic, and functions. The key alternative here is Get-Only Properties, which are well-named to maintain the ___domain-driven language, and enable the continued use of the natural <code>&&</code> operator, instead of the Specification Pattern's <code>And()</code> function. Furthermore, the creation of a well-named function <code>SendToCollectionIfNecessary</code> is potentially more useful and descriptive, than the previous example (which could also be contained in such a function, except not directly on the object apparently).

==References==