A common chore in developing real-world C# applications is implementing value semantics for equality. This involves implementing IEquatable<T>
, overriding Equals()
and GetHashCode()
, and overloading the ==
and !=
operators.
Implementing these methods is a time-consuming and repetitive task, and is easy to get wrong, especially GetHashCode()
. In particular, the best way implement GetHashCode() is much more complicated than
return x.GetHashCode() ^ y.GetHashCode()
.
To simplify this task, I created a ValueComparer
class:
///<summary> /// Contains all of the properties of a class that /// are used to provide value semantics. ///</summary> ///<remarks> /// You can create a static readonly ValueComparer for your class, /// then call into it from Equals, GetHashCode, and CompareTo. ///</remarks> class ValueComparer<T> : IComparer<T>, IEqualityComparer<T> { public ValueComparer(params Func<T, object>[] props) { Properties = new ReadOnlyCollection<Func<T, object>>(props); } public ReadOnlyCollection<Func<T, object>> Properties { get; private set; } public bool Equals(T x, T y) { if (ReferenceEquals(x, y)) return true; if (x == null || y == null) return false; //Object.Equals handles strings and nulls correctly return Properties.All(f => Equals(f(x), f(y))); } //http://stackoverflow.com/questions/263400/263416#263416 public int GetHashCode(T obj) { if (obj == null) return -42; unchecked { int hash = 17; foreach (var prop in Properties) { object value = prop(obj); if (value == null) hash = hash * 23 - 1; else hash = hash * 23 + value.GetHashCode(); } return hash; } } public int Compare(T x, T y) { foreach (var prop in Properties) { //The properties can be any type including null. var comp = Comparer.DefaultInvariant .Compare(prop(x), prop(y)); if (comp != 0) return comp; } return 0; } }
This class implements an external comparer that compares two instances by an ordered list of properties.
ValueComparer can be used as a standalone IComparer<T>
or IEqualityComparer<T>
implementation.
It can also be used to implement value semantics within a type.
For example:
class Person : IComparable<Person>, IEquatable<Person>, IComparable { public string FirstName { get; set; } public string LastName { get; set; } public string Address { get; set; } public string Phone { get; set; } public string Email { get; set; } public override int GetHashCode() { return Comparer.GetHashCode(this); } public int CompareTo(Person obj) { return Comparer.Compare(this, obj); } int IComparable.CompareTo(object obj) { return CompareTo(obj as Person); } public bool Equals(Person obj) { return Comparer.Equals(this, obj); } public override bool Equals(object obj) { return Equals(obj as Person); } static readonly ValueComparer<Person> Comparer = new ValueComparer<Person>( o => o.LastName, o => o.FirstName, o => o.Address, o => o.Phone, o => o.Email ); }
To simplify this task, I created a code snippet:
<?xml version="1.0" encoding="utf-8" ?> <CodeSnippets xmlns="http://schemas.microsoft.com/VisualStudio/2005/CodeSnippet"> <CodeSnippet Format="1.0.0"> <Header> <Title>ValueComparer</Title> <Shortcut>vc</Shortcut> <Description>Code snippet for equality methods using ValueComparer</Description> <Author>SLaks</Author> <SnippetTypes> <SnippetType>Expansion</SnippetType> </SnippetTypes> </Header> <Snippet> <Declarations> <Literal Editable="false"> <ID>classname</ID> <ToolTip>Class name</ToolTip> <Default>ClassNamePlaceholder</Default> <Function>ClassName()</Function> </Literal> </Declarations> <Code Language="csharp"> <![CDATA[public override int GetHashCode() { return Comparer.GetHashCode(this); } public int CompareTo($classname$ obj) { return Comparer.Compare(this, obj); } int IComparable.CompareTo(object obj) { return CompareTo(obj as $classname$); } public bool Equals($classname$ obj) { return Comparer.Equals(this, obj); } public override bool Equals(object obj) { return Equals(obj as $classname$); } static readonly ValueComparer<$classname$> Comparer = new ValueComparer<$classname$>( o => o.$end$ );]]> </Code> </Snippet> </CodeSnippet> </CodeSnippets>It can also be downloaded here; save it to My Documents\Visual Studio 2010\Code Snippets\Visual C#\My Code Snippets\
16 comments:
Pasting the ValueComparer class into VS 2010 C# gives me 6 errors.
The type or namespace name 'ReadOnlyCollection' could not be found (are you missing a using directive or an assembly
The type or namespace name 'ReadOnlyCollection' could not be found (are you missing a using directive or an assembly reference?)
Operator '==' cannot be applied to operands of type 'T' and 'T'
foreach statement cannot operate on variables of type 'ReadOnlyCollection>' because 'ReadOnlyCollection>' does not contain a public definition for 'GetEnumerator'
foreach statement cannot operate on variables of type 'ReadOnlyCollection>' because 'ReadOnlyCollection>' does not contain a public definition for 'GetEnumerator'
Using the generic type 'System.Collections.Generic.Comparer' requires 1 type arguments
Adding "using System.Collections.ObjectModel;" got rid of 4 of the errors, related to ReadOnlyCollection not being recognized, leaving me with these 2 errors:
Operator '==' cannot be applied to operands of type 'T' and 'T'
Using the generic type 'System.Collections.Generic.Comparer' requires 1 type arguments
Adding "using System.Collections;" fixes 1 of the remaining two errors. Leaving me with just:
Operator '==' cannot be applied to operands of type 'T' and 'T'
You're right; that's my fault.
I needed to call ReferenceEquals.
I fixed the code in the original post.
Thanks for catching my mistake!
great
I would like to thank you for the great text. Karina
In my opinion, it's very important to read https://samedaypaper.org/blog/narrative-essay-topics if you are looking for narrative essay writing advices. It was helpful for me and my friends when we were students.
Have questions to enter the online casino? Come to our section of rock BGAOC. best real online gambling slots Come and do not get lost. win with us.
https://khalejmovers.com/
https://khalejmovers.com/نقل-عفش-الرياض-جدة-مكة/
https://khalejmovers.com/نقل-اثاث-الرياض-الكويت/
https://khalejmovers.com/نقل-اثاث-الرياض-الامارات/
https://khalejmovers.com/نقل-اثاث-الرياض-الاردن/
https://khalejmovers.com/نقل-اثاث-من-الرياض-الى-الدمام/
https://khalejmovers.com/شركة-ديكور-بالرياض/
https://khalejmovers.com/شركة-دهانات-بالرياض/
hy
thanks for sharing this blog
plz visit Best landscaping company in India
Thanks for this important information through your website. QuickBooks Firewall Error acts as a barrier between the quickbooks company file and quickbooks desktop. It doesn't allow the quickbooks software to communicate with the quickbooks company file and this error has been experienced by the users many times.quickbooks database server manager windows firewall is blocking quickbooks
Money market There is no need to be physically present for trading securities, as one can trade from anywhere through the internet or telephone
Merkur 15c Safety Razor - Barber Pole - Deccasino
Merkur casinosites.one 15C Safety Razor - casino-roll.com Merkur - https://deccasino.com/review/merit-casino/ 15C for https://jancasino.com/review/merit-casino/ Barber Pole is the 바카라 사이트 perfect introduction to the Merkur Safety Razor.
This blog post is really amazing! It may be quite difficult to navigate the complicated divorce process, but your short and to-the-point information on how to file for divorce in New York is really beneficial. Finding a source that offers helpful information in such a good manner is reassuring. I appreciate you bringing light on this very difficult subject!Solicite el Divorcio en Nueva York
pgaztec เกมแตกดี ที่สุด ในตอนนี้ เป็นหนึ่งในเกมสล็อตที่ได้รับความนิยมจากผู้เล่นมากมาย เกมนี้มีธีมที่น่าสนใจจากชุดหุ่นของชนบทและวัฒนธรรมอะซเทคจาก pg slot ซึ่งนำเสนอบรรยากาศ
Simplifying value comparison semantics involves streamlining the process of comparing values or variables in a programming context, often by reducing complexity and increasing readability. This simplification may entail using clear and concise syntax, employing built-in functions or operators for comparisons, and minimizing unnecessary conditions or logic to enhance code efficiency and maintainability
bufete de abogados de accidentes de motocicleta
tax and estate lawyer
Improved readability: Simplifying value comparison semantics ensures that code is more intuitive ||abogado de delitos sexuales nueva jersey||Getting Divorced in New York City and easier to understand for developers.
Post a Comment