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{{shortShort description|Software design pattern}}
[[ImageFile:Specification UML.png|right|thumb|300px|Specification Pattern in [[Unified Modeling Language|UML]] ]]
In computer programming, the '''specification pattern''' is a particular [[software design pattern]], whereby [[business rules]] can be recombined by chaining the business rules together using [[boolean algebra|boolean logic]]. The pattern is frequently used in the context of [[___domain-driven design]].
 
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== Code examples ==
 
=== [[C Sharp (programming language)|C#]] ===
{{Further|C Sharp (programming language)}}
 
<syntaxhighlight lang="csharp">
public interface ISpecification
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public class AndSpecification : CompositeSpecification
{
private ISpecification leftCondition_leftCondition;
private ISpecification rightCondition_rightCondition;
 
public AndSpecification(ISpecification left, ISpecification right)
{
leftCondition_leftCondition = left;
rightCondition_rightCondition = right;
}
 
public override bool IsSatisfiedBy(object candidate)
{
return leftCondition_leftCondition.IsSatisfiedBy(candidate) && rightCondition_rightCondition.IsSatisfiedBy(candidate);
}
}
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public class AndNotSpecification : CompositeSpecification
{
private ISpecification leftCondition_leftCondition;
private ISpecification rightCondition_rightCondition;
 
public AndNotSpecification(ISpecification left, ISpecification right)
{
leftCondition_leftCondition = left;
rightCondition_rightCondition = right;
}
 
public override bool IsSatisfiedBy(object candidate)
{
return leftCondition_leftCondition.IsSatisfiedBy(candidate) && rightCondition_rightCondition.IsSatisfiedBy(candidate) != true;
}
}
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public class OrSpecification : CompositeSpecification
{
private ISpecification leftCondition_leftCondition;
private ISpecification rightCondition_rightCondition;
 
public OrSpecification(ISpecification left, ISpecification right)
{
leftCondition_leftCondition = left;
rightCondition_rightCondition = right;
}
 
public override bool IsSatisfiedBy(object candidate)
{
return leftCondition_leftCondition.IsSatisfiedBy(candidate) || rightCondition_rightCondition.IsSatisfiedBy(candidate);
}
}
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public class OrNotSpecification : CompositeSpecification
{
private ISpecification leftCondition_leftCondition;
private ISpecification rightCondition_rightCondition;
 
public OrNotSpecification(ISpecification left, ISpecification right)
{
leftCondition_leftCondition = left;
rightCondition_rightCondition = right;
}
 
public override bool IsSatisfiedBy(object candidate)
{
return leftCondition_leftCondition.IsSatisfiedBy(candidate) || rightCondition_rightCondition.IsSatisfiedBy(candidate) != true;
}
}
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public class NotSpecification : CompositeSpecification
{
private ISpecification Wrapped_wrapped;
 
public NotSpecification(ISpecification x)
{
Wrapped_wrapped = x;
}
 
public override bool IsSatisfiedBy(object candidate)
{
return !Wrapped_wrapped.IsSatisfiedBy(candidate);
}
}
</syntaxhighlight>
 
=== [[C Sharp (programming language)|C# 6.0]] with generics ===
{{Further|C Sharp (programming language)}}
 
<syntaxhighlight lang="csharp">
public interface ISpecification<T>
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public class AndSpecification<T> : CompositeSpecification<T>
{
private ISpecification<T> left_left;
private ISpecification<T> right_right;
 
public AndSpecification(ISpecification<T> left, ISpecification<T> right)
{
this.left_left = left;
this.right_right = right;
}
 
public override bool IsSatisfiedBy(T candidate) => left_left.IsSatisfiedBy(candidate) && right_right.IsSatisfiedBy(candidate);
}
 
public class AndNotSpecification<T> : CompositeSpecification<T>
{
private ISpecification<T> left_left;
private ISpecification<T> right_right;
 
public AndNotSpecification(ISpecification<T> left, ISpecification<T> right)
{
this.left_left = left;
this.right_right = right;
}
 
public override bool IsSatisfiedBy(T candidate) => left_left.IsSatisfiedBy(candidate) && !right_right.IsSatisfiedBy(candidate);
}
 
public class OrSpecification<T> : CompositeSpecification<T>
{
private ISpecification<T> left_left;
private ISpecification<T> right_right;
 
public OrSpecification(ISpecification<T> left, ISpecification<T> right)
{
this.left_left = left;
this.right_right = right;
}
 
public override bool IsSatisfiedBy(T candidate) => left_left.IsSatisfiedBy(candidate) || right_right.IsSatisfiedBy(candidate);
}
public class OrNotSpecification<T> : CompositeSpecification<T>
{
private ISpecification<T> left_left;
private ISpecification<T> right_right;
 
public OrNotSpecification(ISpecification<T> left, ISpecification<T> right)
{
this.left_left = left;
this.right_right = right;
}
 
public override bool IsSatisfiedBy(T candidate) => left_left.IsSatisfiedBy(candidate) || !right_right.IsSatisfiedBy(candidate);
}
 
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</syntaxhighlight>
 
=== [[Python (programming language)|Python]] ===
{{Further|Python (programming language)}}
<syntaxhighlight lang="python">
from abc import ABC, abstractmethod
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</syntaxhighlight>
 
=== [[C++ (programming language)|C++]] ===
{{Further|C++}}
<syntaxhighlight lang="cpp">
template <class T>
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</syntaxhighlight>
 
=== [[TypeScript]] ===
{{Further|TypeScript}}
 
<syntaxhighlight lang="typescript">
export interface ISpecification {
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==Example of use==
 
In the followingnext example, weinvoices are retrieving invoicesretrieved and sending themsent to a collection agency if:
 
# they are overdue,
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<syntaxhighlight lang="csharp">
var overDueoverdue = new OverDueSpecificationOverdueSpecification();
var noticeSent = new NoticeSentSpecification();
var inCollection = new InCollectionSpecification();
 
// Example of specification pattern logic chaining
var sendToCollection = overDueoverdue.And(noticeSent).And(inCollection.Not());
 
var invoiceCollectioninvoices = ServiceInvoiceService.GetInvoices();
 
foreach (var currentInvoiceinvoice in invoiceCollectioninvoices)
{
if (sendToCollection.IsSatisfiedBy(currentInvoiceinvoice))
{
currentInvoiceinvoice.SendToCollection();
}
}
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* [https://web.archive.org/web/20110724151447/http://www.dpdk.nl/opensource/specification-pattern-for-selection-on-lists specification pattern in flash actionscript 3] by Rolf Vreijdenberger
 
{{Design Patterns Patternspatterns}}
 
[[Category:Architectural pattern (computer science)]]
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