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IEquatable<T> F# snippets (#7767)
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‎snippets/fsharp/System/IEquatableT/Equals/EqualsEx2.fs

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module EqualsEx2
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// <Snippet3>
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open System
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open System.Text.RegularExpressions
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type Person(lastName, ssn) =
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let mutable lastName = lastName
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let ssn =
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if Regex.IsMatch(ssn, @"\d{9}") then
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$"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}"
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elif Regex.IsMatch(ssn, @"\d{3}-\d{2}-\d{4}") then
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ssn
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else
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raise (FormatException "The social security number has an invalid format.")
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member _.SSN =
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ssn
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member _.LastName
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with get () = lastName
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and set (value) =
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if String.IsNullOrEmpty value then
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invalidArg (nameof value) "The last name cannot be null or empty."
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else
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lastName <- value
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static member op_Equality (person1: Person, person2: Person) =
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if box person1 |> isNull || box person2 |> isNull then
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Object.Equals(person1, person2)
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else
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person1.Equals person2
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static member op_Inequality (person1: Person, person2: Person) =
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if box person1 |> isNull || box person2 |> isNull then
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Object.Equals(person1, person2) |> not
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else
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person1.Equals person2 |> not
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override _.GetHashCode() =
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ssn.GetHashCode()
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override this.Equals(obj: obj) =
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match obj with
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| :? Person as personObj ->
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(this :> IEquatable<_>).Equals personObj
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| _ -> false
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interface IEquatable<Person> with
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member this.Equals(other: Person) =
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match box other with
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| null -> false
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| _ ->
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this.SSN = other.SSN
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// </Snippet3>
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// Create a Person object for each job applicant.
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let applicant1 = Person("Jones", "099-29-4999")
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let applicant2 = Person("Jones", "199-29-3999")
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let applicant3 = Person("Jones", "299-49-6999")
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// Add applicants to a List object.
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let applicants = ResizeArray()
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applicants.Add applicant1
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applicants.Add applicant2
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applicants.Add applicant3
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// Create a Person object for the final candidate.
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let candidate = Person("Jones", "199-29-3999")
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if applicants.Contains candidate then
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printfn $"Found {candidate.LastName} (SSN {candidate.SSN})."
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else
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printfn $"Applicant {candidate.SSN} not found."
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// Call the shared inherited Equals(Object, Object) method.
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// It will in turn call the IEquatable<T>.Equals implementation.
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printfn $"{applicant2.LastName}({applicant2.SSN}) already on file: {Person.Equals(applicant2, candidate)}."
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// The example displays the following output:
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// Found Jones (SSN 199-29-3999).
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// Jones(199-29-3999) already on file: True.
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// This tests the handling of null values, but does not appear in the documentation.
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//
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//public class Example
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//{
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// public static void Main()
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// {
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// var p1 = new Person("Joe", "613-24-0068")
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// Person p2 = null
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//
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// Console.WriteLine(p1 == p2)
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// }
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//}

‎snippets/fsharp/System/IEquatableT/Equals/Snippet12.fs

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open System
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open System.Collections.Generic
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open System.Text.RegularExpressions
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type Person(lastName, ssn) =
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let mutable lastName = lastName
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let ssn =
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if Regex.IsMatch(ssn, @"\d{9}") then
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$"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}"
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elif Regex.IsMatch(ssn, @"\d{3}-\d{2}-\d{4}") then
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ssn
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else
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raise (FormatException "The social security number has an invalid format.")
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member _.SSN =
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ssn
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member _.LastName
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with get () = lastName
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and set (value) =
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if String.IsNullOrEmpty value then
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invalidArg (nameof value) "The last name cannot be null or empty."
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else
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lastName <- value
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static member op_Equality (person1: Person, person2: Person) =
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if box person1 |> isNull || box person2 |> isNull then
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Object.Equals(person1, person2)
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else
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person1.Equals person2
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static member op_Inequality (person1: Person, person2: Person) =
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if box person1 |> isNull || box person2 |> isNull then
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Object.Equals(person1, person2) |> not
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else
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person1.Equals person2 |> not
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override _.GetHashCode() =
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ssn.GetHashCode()
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override this.Equals(obj: obj) =
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match obj with
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| :? Person as personObj ->
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(this :> IEquatable<_>).Equals personObj
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| _ -> false
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interface IEquatable<Person> with
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member this.Equals(other: Person) =
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match box other with
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| null -> false
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| _ ->
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this.SSN = other.SSN
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// <Snippet12>
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// Create a Person object for each job applicant.
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let applicant1 = Person("Jones", "099-29-4999")
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let applicant2 = Person("Jones", "199-29-3999")
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let applicant3 = Person("Jones", "299-49-6999")
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// Add applicants to a List object.
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let applicants = ResizeArray()
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applicants.Add applicant1
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applicants.Add applicant2
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applicants.Add applicant3
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// Create a Person object for the final candidate.
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let candidate = Person("Jones", "199-29-3999")
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if applicants.Contains candidate then
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printfn $"Found {candidate.LastName} (SSN {candidate.SSN})."
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else
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printfn $"Applicant {candidate.SSN} not found."
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// Call the shared inherited Equals(Object, Object) method.
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// It will in turn call the IEquatable<T>.Equals implementation.
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printfn $"{applicant2.LastName}({applicant2.SSN}) already on file: {Person.Equals(applicant2, candidate)}."
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// The example displays the following output:
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// Found Jones (SSN 199-29-3999).
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// Jones(199-29-3999) already on file: True.
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// </Snippet12>

‎snippets/fsharp/System/IEquatableT/Equals/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="EqualsEx2.fs" />
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<Compile Include="Snippet12.fs" />
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</ItemGroup>
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</Project>

‎xml/System/IEquatable`1.xml

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The following example shows the partial implementation of a `Person` class that implements <xref:System.IEquatable%601> and has two properties, `LastName` and `SSN`. The <xref:System.IEquatable%601.Equals%2A> method returns `True` if the `SSN` property of two `Person` objects is identical; otherwise, it returns `False`.
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:::code language="csharp" source="~/snippets/csharp/System/IEquatableT/Equals/EqualsEx2.cs" id="Snippet3":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IEquatableT/Equals/EqualsEx2.fs" id="Snippet3":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.GenericIEquatable.Equals/vb/EqualsEx2.vb" id="Snippet3":::
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`Person` objects can then be stored in a <xref:System.Collections.Generic.List%601> object and can be identified by the `Contains` method, as the following example shows.
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:::code language="csharp" source="~/snippets/csharp/System/IEquatableT/Equals/Snippet12.cs" id="Snippet12":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IEquatableT/Equals/Snippet12.fs" id="Snippet12":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.GenericIEquatable.Equals/vb/Snippet12.vb" id="Snippet12":::
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]]></format>

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