HashCode Estrutura

Definição

Espaço de Nomes:
System
Assemblagem:
netstandard.dll

Combina o código de hash de múltiplos valores num único código de hash.

public value class HashCode
public struct HashCode
type HashCode = struct
Public Structure HashCode
Herança
Object
ValueType
HashCode

Exemplos

Os métodos estáticos desta classe combinam os códigos de hash padrão de até oito valores.

using System;
using System.Collections.Generic;

public struct OrderOrderLine : IEquatable<OrderOrderLine>
{
    public int OrderId { get; }
    public int OrderLineId { get; }

    public OrderOrderLine(int orderId, int orderLineId) => (OrderId, OrderLineId) = (orderId, orderLineId);

    public override bool Equals(object obj) => obj is OrderOrderLine o && Equals(o);

    public bool Equals(OrderOrderLine other) => OrderId == other.OrderId && OrderLineId == other.OrderLineId;

    public override int GetHashCode() => HashCode.Combine(OrderId, OrderLineId);
}

class Program
{
    static void Main(string[] args)
    {
        var set = new HashSet<OrderOrderLine>
        {
            new OrderOrderLine(1, 1),
            new OrderOrderLine(1, 1),
            new OrderOrderLine(1, 2)
        };

        Console.WriteLine($"Item count: {set.Count}.");
    }
}
// The example displays the following output:
// Item count: 2.

open System
open System.Collections.Generic

[<Struct; CustomEquality; NoComparison>]
type OrderOrderLine(orderId: int, orderLineId: int) =
    member _.OrderId = orderId
    member _.OrderLineId = orderLineId

    override _.GetHashCode() = 
        HashCode.Combine(orderId, orderLineId)

    override this.Equals(obj) =
        match obj with
        | :? OrderOrderLine as o -> (this :> IEquatable<_>).Equals o
        | _ -> false

    interface IEquatable<OrderOrderLine> with
        member _.Equals(other: OrderOrderLine) = 
            orderId = other.OrderId && orderLineId = other.OrderLineId

let set =
    HashSet<OrderOrderLine> [ OrderOrderLine(1, 1); OrderOrderLine(1, 1); OrderOrderLine(1, 2) ]
printfn $"Item count: {set.Count}."

// The example displays the following output:
// Item count: 2.

Public Structure OrderOrderLine
    Implements IEquatable(Of OrderOrderLine)

    Public ReadOnly Property OrderId As Integer
    Public ReadOnly Property OrderLineId As Integer

    Public Sub New(ByVal orderId As Integer, ByVal orderLineId As Integer)
        Me.OrderId = orderId
        Me.OrderLineId = orderLineId
    End Sub

    Public Overrides Function Equals(obj As Object) As Boolean
        Return (TypeOf obj Is OrderOrderLine) AndAlso Equals(DirectCast(obj, OrderOrderLine))
    End Function

    Public Overloads Function Equals(other As OrderOrderLine) As Boolean Implements IEquatable(Of OrderOrderLine).Equals
        Return OrderId = other.OrderId AndAlso
               OrderLineId = other.OrderLineId
    End Function

    Public Overrides Function GetHashCode() As Integer
        Return HashCode.Combine(OrderId, OrderLineId)
    End Function

End Structure

Module Program

    Sub Main(args As String())
        Dim hashSet As HashSet(Of OrderOrderLine) = New HashSet(Of OrderOrderLine)
        hashSet.Add(New OrderOrderLine(1, 1))
        hashSet.Add(New OrderOrderLine(1, 1))
        hashSet.Add(New OrderOrderLine(1, 2))
        Console.WriteLine($"Item count: {hashSet.Count}")
    End Sub

End Module
' The example displays the following output:
' Item count: 2.

Importante

ToHashCode() deve ser chamado no máximo uma vez por cada instância de HashCode.

Os métodos de instância nesta classe combinam os códigos de hash de mais de oito valores.

using System;
using System.Collections.Generic;

public struct Path : IEquatable<Path>
{
    public IReadOnlyList<string> Segments { get; }

    public Path(params string[] segments) => Segments = segments;

    public override bool Equals(object obj) => obj is Path o && Equals(o);

    public bool Equals(Path other)
    {
        if (ReferenceEquals(Segments, other.Segments)) return true;
        if (Segments is null || other.Segments is null) return false;
        if (Segments.Count != other.Segments.Count) return false;

        for (var i = 0; i < Segments.Count; i++)
        {
            if (!string.Equals(Segments[i], other.Segments[i]))
                return false;
        }

        return true;
    }

    public override int GetHashCode()
    {
        var hash = new HashCode();

        for (var i = 0; i < Segments?.Count; i++)
            hash.Add(Segments[i]);

        return hash.ToHashCode();
    }
}

class Program
{
    static void Main(string[] args)
    {
        var set = new HashSet<Path>
        {
            new Path("C:", "tmp", "file.txt"),
            new Path("C:", "tmp", "file.txt"),
            new Path("C:", "tmp", "file.tmp")
        };

        Console.WriteLine($"Item count: {set.Count}.");
    }
}
// The example displays the following output:
// Item count: 2.

open System
open System.Collections.Generic

[<Struct; CustomEquality; NoComparison>]
type Path([<ParamArray>]segments: string[]) = 
    member _.Segments = 
        Array.AsReadOnly segments

    override this.Equals(obj) =
        match obj with
        | :? Path as o -> (this :> IEquatable<_>).Equals(o)
        | _ -> false

    interface IEquatable<Path> with
        member this.Equals(other: Path) =
            Object.ReferenceEquals(this.Segments, other.Segments) ||
            not (isNull this.Segments) && 
            not (isNull other.Segments) &&
            this.Segments.Count = other.Segments.Count &&
            Seq.forall2 (=) this.Segments other.Segments 

    override this.GetHashCode() =
        let hash = HashCode()

        for i = 0 to this.Segments.Count - 1 do
            hash.Add this.Segments[i]
        hash.ToHashCode()

let set = 
    HashSet<Path> [
        Path("C:", "tmp", "file.txt")
        Path("C:", "tmp", "file.tmp")
        Path("C:", "tmp", "file.txt") ]
        
printfn $"Item count: {set.Count}."

// The example displays the following output:
// Item count: 2.

Public Structure Path
    Implements IEquatable(Of Path)

    Public ReadOnly Property Segments As IReadOnlyList(Of String)

    Public Sub New(ParamArray ByVal segments() As String)
        Me.Segments = segments
    End Sub

    Public Overrides Function Equals(obj As Object) As Boolean
        Return (TypeOf obj Is Path) AndAlso Equals(DirectCast(obj, Path))
    End Function

    Public Overloads Function Equals(other As Path) As Boolean Implements IEquatable(Of Path).Equals
        If ReferenceEquals(Segments, other.Segments) Then Return True
        If Segments Is Nothing OrElse other.Segments Is Nothing Then Return False
        If Segments.Count <> other.Segments.Count Then Return False

        For i As Integer = 0 To Segments.Count - 1
            If Not String.Equals(Segments(i), other.Segments(i)) Then Return False
        Next

        Return True
    End Function

    Public Overrides Function GetHashCode() As Integer
        Dim hash As HashCode = New HashCode()

        For i As Integer = 0 To Segments?.Count - 1
            hash.Add(Segments(i))
        Next

        Return hash.ToHashCode()
    End Function

End Structure

Module Program

    Sub Main(args As String())
        Dim hashSet As HashSet(Of Path) = New HashSet(Of Path) From {
            New Path("C:", "tmp", "file.txt"),
            New Path("C:", "tmp", "file.txt"),
            New Path("C:", "tmp", "file.tmp")
        }
        Console.WriteLine($"Item count: {hashSet.Count}.")
    End Sub

End Module
' The example displays the following output:
' Item count: 2.

Os métodos de instância também combinam os códigos de hash produzidos por uma implementação específica IEqualityComparer<T> .

using System;
using System.Collections.Generic;

public struct Path : IEquatable<Path>
{
    public IReadOnlyList<string> Segments { get; }

    public Path(params string[] segments) => Segments = segments;

    public override bool Equals(object obj) => obj is Path o && Equals(o);

    public bool Equals(Path other)
    {
        if (ReferenceEquals(Segments, other.Segments)) return true;
        if (Segments is null || other.Segments is null) return false;
        if (Segments.Count != other.Segments.Count) return false;

        for (var i = 0; i < Segments.Count; i++)
        {
            if (!string.Equals(Segments[i], other.Segments[i], StringComparison.OrdinalIgnoreCase))
                return false;
        }

        return true;
    }

    public override int GetHashCode()
    {
        var hash = new HashCode();

        for (var i = 0; i < Segments?.Count; i++)
            hash.Add(Segments[i], StringComparer.OrdinalIgnoreCase);

        return hash.ToHashCode();
    }
}

class Program
{
    static void Main(string[] args)
    {
        var set = new HashSet<Path>
        {
            new Path("C:", "tmp", "file.txt"),
            new Path("C:", "TMP", "file.txt"),
            new Path("C:", "tmp", "FILE.TXT")
        };

        Console.WriteLine($"Item count: {set.Count}.");
    }
}
// The example displays the following output:
// Item count: 1.

open System
open System.Collections.Generic

[<Struct; CustomEquality; NoComparison>]
type Path([<ParamArray>]segments: string[]) =
    member _.Segments = 
        Array.AsReadOnly segments

    override this.Equals(obj) =
        match obj with
        | :? Path as o -> (this :> IEquatable<_>).Equals(o)
        | _ -> false

    interface IEquatable<Path> with
        member this.Equals(other: Path) =
            Object.ReferenceEquals(this.Segments, other.Segments) ||
            not (isNull this.Segments) && 
            not (isNull other.Segments) &&
            this.Segments.Count = other.Segments.Count &&
            Seq.forall2 (fun x y -> String.Equals(x, y, StringComparison.OrdinalIgnoreCase)) this.Segments other.Segments 

    override this.GetHashCode() =
        let hash = HashCode()

        for i = 0 to this.Segments.Count - 1 do
            hash.Add(this.Segments[i], StringComparer.OrdinalIgnoreCase)
        hash.ToHashCode()

let set = 
    HashSet<Path> [
        Path("C:", "tmp", "file.txt")
        Path("C:", "tmp", "file.tmp")
        Path("C:", "tmp", "file.txt") ]

printfn $"Item count: {set.Count}."

// The example displays the following output:
// Item count: 1.

Public Structure Path
    Implements IEquatable(Of Path)

    Public ReadOnly Property Segments As IReadOnlyList(Of String)

    Public Sub New(ParamArray ByVal segments() As String)
        Me.Segments = segments
    End Sub

    Public Overrides Function Equals(obj As Object) As Boolean
        Return (TypeOf obj Is Path) AndAlso Equals(DirectCast(obj, Path))
    End Function

    Public Overloads Function Equals(other As Path) As Boolean Implements IEquatable(Of Path).Equals
        If ReferenceEquals(Segments, other.Segments) Then Return True
        If Segments Is Nothing OrElse other.Segments Is Nothing Then Return False
        If Segments.Count <> other.Segments.Count Then Return False

        For i As Integer = 0 To Segments.Count - 1
            If Not String.Equals(Segments(i), other.Segments(i), StringComparison.OrdinalIgnoreCase) Then Return False
        Next

        Return True
    End Function

    Public Overrides Function GetHashCode() As Integer
        Dim hash As HashCode = New HashCode()

        For i As Integer = 0 To Segments?.Count - 1
            hash.Add(Segments(i), StringComparer.OrdinalIgnoreCase)
        Next

        Return hash.ToHashCode()
    End Function
    
End Structure

Module Program

    Sub Main(args As String())
        Dim hashSet As HashSet(Of Path) = New HashSet(Of Path) From {
            New Path("C:", "tmp", "file.txt"),
            New Path("C:", "TMP", "file.txt"),
            New Path("C:", "tmp", "FILE.TXT")
        }
        Console.WriteLine($"Item count: {hashSet.Count}.")
    End Sub

End Module
' The example displays the following output:
' Item count: 1.

A HashCode estrutura deve ser passada por referência a outros métodos, pois é um tipo de valor.

using System;
using System.Collections.Generic;

public struct Path : IEquatable<Path>
{
    public IReadOnlyList<string> Segments { get; }

    public Path(params string[] segments) => Segments = segments;

    public override bool Equals(object obj) => obj is Path o && Equals(o);

    public bool Equals(Path other)
    {
        if (ReferenceEquals(Segments, other.Segments)) return true;
        if (Segments is null || other.Segments is null) return false;
        if (Segments.Count != other.Segments.Count) return false;

        for (var i = 0; i < Segments.Count; i++)
        {
            if (!PlatformUtils.PathEquals(Segments[i], other.Segments[i]))
                return false;
        }

        return true;
    }

    public override int GetHashCode()
    {
        var hash = new HashCode();

        for (var i = 0; i < Segments?.Count; i++)
            PlatformUtils.AddPath(ref hash, Segments[i]);

        return hash.ToHashCode();
    }
}

internal static class PlatformUtils
{
    public static bool PathEquals(string a, string b) => string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
    public static void AddPath(ref HashCode hash, string path) => hash.Add(path, StringComparer.OrdinalIgnoreCase);
}

class Program
{
    static void Main(string[] args)
    {
        var set = new HashSet<Path>
        {
            new Path("C:", "tmp", "file.txt"),
            new Path("C:", "TMP", "file.txt"),
            new Path("C:", "tmp", "FILE.TXT")
        };

        Console.WriteLine($"Item count: {set.Count}.");
    }
}
// The example displays the following output:
// Item count: 1.

open System
open System.Collections.Generic

module PlatformUtils =
    let pathEquals a b = String.Equals(a, b, StringComparison.OrdinalIgnoreCase)
    let addPath (hash: byref<HashCode>) path = hash.Add(path, StringComparer.OrdinalIgnoreCase)

[<Struct; CustomEquality; NoComparison>]
type Path([<ParamArray>]segments: string[]) =
    member _.Segments = 
        Array.AsReadOnly segments

    override this.Equals(obj) =
        match obj with
        | :? Path as o -> (this :> IEquatable<_>).Equals(o)
        | _ -> false

    interface IEquatable<Path> with
        member this.Equals(other: Path) =
            Object.ReferenceEquals(this.Segments, other.Segments) ||
            not (isNull this.Segments) && 
            not (isNull other.Segments) &&
            this.Segments.Count = other.Segments.Count &&
            Seq.forall2 PlatformUtils.pathEquals this.Segments other.Segments 

    override this.GetHashCode() =
        let mutable hash = HashCode()

        for i = 0 to this.Segments.Count - 1 do
            PlatformUtils.addPath &hash this.Segments[i]
        hash.ToHashCode()


let set =
    HashSet<Path> [
        Path("C:", "tmp", "file.txt")
        Path("C:", "TMP", "file.txt")
        Path("C:", "tmp", "FILE.TXT") ]

printfn $"Item count: {set.Count}."

// The example displays the following output:
// Item count: 1.

Public Structure Path
    Implements IEquatable(Of Path)

    Public ReadOnly Property Segments As IReadOnlyList(Of String)

    Public Sub New(ParamArray ByVal segments() As String)
        Me.Segments = segments
    End Sub

    Public Overrides Function Equals(obj As Object) As Boolean
        Return (TypeOf obj Is Path) AndAlso Equals(DirectCast(obj, Path))
    End Function

    Public Overloads Function Equals(other As Path) As Boolean Implements IEquatable(Of Path).Equals
        If ReferenceEquals(Segments, other.Segments) Then Return True
        If Segments Is Nothing OrElse other.Segments Is Nothing Then Return False
        If Segments.Count <> other.Segments.Count Then Return False

        For i As Integer = 0 To Segments.Count - 1
            If Not PathEquals(Segments(i), other.Segments(i)) Then Return False
        Next

        Return True
    End Function

    Public Overrides Function GetHashCode() As Integer
        Dim hash As HashCode = New HashCode()

        For i As Integer = 0 To Segments?.Count - 1
            AddPath(hash, Segments(i))
        Next

        Return hash.ToHashCode()
    End Function
    
End Structure

Friend Module PlatformUtils

    Public Function PathEquals(ByVal a As String, ByVal b As String) As Boolean
        Return String.Equals(a, b, StringComparison.OrdinalIgnoreCase)
    End Function

    Public Sub AddPath(ByRef hash As HashCode, ByVal path As String)
        hash.Add(path, StringComparer.OrdinalIgnoreCase)
    End Sub

End Module

Module Program

    Sub Main(args As String())
        Dim hashSet As HashSet(Of Path) = New HashSet(Of Path) From {
            New Path("C:", "tmp", "file.txt"),
            New Path("C:", "TMP", "file.txt"),
            New Path("C:", "tmp", "FILE.TXT")
        }
        Console.WriteLine($"Item count: {hashSet.Count}.")
    End Sub

End Module
' The example displays the following output:
' Item count: 1.

Observações

Pode combinar HashCode vários valores (por exemplo, campos numa estrutura ou classe) num único código hash. Esta estrutura tem métodos estáticos e de instância que funcionam de forma diferente:

  • Os métodos estáticos aceitam um conjunto de até oito valores para combinar.
  • Os métodos de duas instâncias funcionam de forma contínua, aceitando valores um de cada vez.

Warning

É uma boa prática considerar os códigos hash como um detalhe de implementação, pois a implementação pode mudar entre versões de assembly. Não armazene códigos hash produzidos em HashCode estruturas serializadas, por exemplo, no disco. HashCode utiliza uma semente aleatória inicializada estaticamente para impor esta melhor prática, o que significa que os códigos de hash são apenas determinísticos dentro do âmbito de um processo do sistema operativo.

Métodos

Name Description
Add<T>(T, IEqualityComparer<T>)

Adiciona um único valor ao código de hash, especificando o tipo que fornece a função de código de hash.
Add<T>(T)

Adiciona um único valor ao código hash.
Combine<T1,T2,T3,T4,T5,T6,T7,T8>(T1, T2, T3, T4, T5, T6, T7, T8)

Combina oito valores num código hash.
Combine<T1,T2,T3,T4,T5,T6,T7>(T1, T2, T3, T4, T5, T6, T7)

Combina sete valores num código hash.
Combine<T1,T2,T3,T4,T5,T6>(T1, T2, T3, T4, T5, T6)

Combina seis valores num código hash.
Combine<T1,T2,T3,T4,T5>(T1, T2, T3, T4, T5)

Combina cinco valores num código hash.
Combine<T1,T2,T3,T4>(T1, T2, T3, T4)

Combina quatro valores num código hash.
Combine<T1,T2,T3>(T1, T2, T3)

Combina três valores num código hash.
Combine<T1,T2>(T1, T2)

Combina dois valores num código hash.
Combine<T1>(T1)

Dispersa o código de hash devolvido pelo valor especificado.
Equals(Object)
Obsoleto.

Este método não é suportado e não deve ser chamado.
GetHashCode()
Obsoleto.

Este método não é suportado e não deve ser chamado.
ToHashCode()

Calcula o código hash final após invocações consecutivas Add .

Aplica-se a