Func<T1,T2,T3,TResult> Delegate
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Encapsulates a method that has three parameters and returns a value of the type specified by the TResult
parameter.
generic <typename T1, typename T2, typename T3, typename TResult>
public delegate TResult Func(T1 arg1, T2 arg2, T3 arg3);
public delegate TResult Func<in T1,in T2,in T3,out TResult>(T1 arg1, T2 arg2, T3 arg3);
public delegate TResult Func<T1,T2,T3,TResult>(T1 arg1, T2 arg2, T3 arg3);
type Func<'T1, 'T2, 'T3, 'Result> = delegate of 'T1 * 'T2 * 'T3 -> 'Result
Public Delegate Function Func(Of In T1, In T2, In T3, Out TResult)(arg1 As T1, arg2 As T2, arg3 As T3) As TResult
Public Delegate Function Func(Of T1, T2, T3, TResult)(arg1 As T1, arg2 As T2, arg3 As T3) As TResult
- T1
The type of the first parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T2
The type of the second parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T3
The type of the third parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- TResult
The type of the return value of the method that this delegate encapsulates.
This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- arg1
- T1
The first parameter of the method that this delegate encapsulates.
- arg2
- T2
The second parameter of the method that this delegate encapsulates.
- arg3
- T3
The third parameter of the method that this delegate encapsulates.
The return value of the method that this delegate encapsulates.
The following example demonstrates how to declare and use a Func<T1,T2,TResult> delegate. This example declares a Func<T1,T2,TResult> variable and assigns it a lambda expression that takes a String value and an Int32 value as parameters. The lambda expression returns true
if the length of the String parameter is equal to the value of the Int32 parameter. The delegate that encapsulates this method is subsequently used in a query to filter strings in an array of strings.
using System;
using System.Collections.Generic;
using System.Linq;
public class Func3Example
{
public static void Main()
{
Func<String, int, bool> predicate = (str, index) => str.Length == index;
String[] words = { "orange", "apple", "Article", "elephant", "star", "and" };
IEnumerable<String> aWords = words.Where(predicate).Select(str => str);
foreach (String word in aWords)
Console.WriteLine(word);
}
}
open System
open System.Linq
let predicate = Func<string, int, bool>(fun str index -> str.Length = index)
let words = [ "orange"; "apple"; "Article"; "elephant"; "star"; "and" ]
let aWords = words.Where predicate
for word in aWords do
printfn $"{word}"
Imports System.Collections.Generic
Imports System.Linq
Public Module Func3Example
Public Sub Main()
Dim predicate As Func(Of String, Integer, Boolean) = Function(str, index) str.Length = index
Dim words() As String = { "orange", "apple", "Article", "elephant", "star", "and" }
Dim aWords As IEnumerable(Of String) = words.Where(predicate)
For Each word As String In aWords
Console.WriteLine(word)
Next
End Sub
End Module
You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have three parameters, each of which is passed to it by value, and that it must return a value.
Примечание
To reference a method that has three parameters and returns void
(unit
in F#) (or in Visual Basic, that is declared as a Sub
rather than as a Function
), use the generic Action<T1,T2,T3> delegate instead.
When you use the Func<T1,T2,T3,TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with three parameters. For example, the following code explicitly declares a generic delegate named ParseNumber
and assigns a reference to the Parse method to its delegate instance.
using System;
using System.Globalization;
delegate T ParseNumber<T>(string input, NumberStyles styles,
IFormatProvider provider);
public class DelegateExample
{
public static void Main()
{
string numericString = "-1,234";
ParseNumber<int> parser = int.Parse;
Console.WriteLine(parser(numericString,
NumberStyles.Integer | NumberStyles.AllowThousands,
CultureInfo.InvariantCulture));
}
}
open System
open System.Globalization
type ParseNumber<'T> = delegate of (string * NumberStyles * IFormatProvider) -> 'T
let numericString = "-1,234"
let parser = ParseNumber<int> Int32.Parse
parser.Invoke(
numericString,
NumberStyles.Integer ||| NumberStyles.AllowThousands,
CultureInfo.InvariantCulture )
|> printfn "%i"
Imports System.Globalization
Delegate Function ParseNumber(Of T)(input As String, styles As NumberStyles, _
provider As IFormatProvider) As T
Module DelegateExample
Public Sub Main()
Dim numericString As String = "-1,234"
Dim parser As ParseNumber(Of Integer) = AddressOf Integer.Parse
Console.WriteLine(parser(numericString, _
NumberStyles.Integer Or NumberStyles.AllowThousands, _
CultureInfo.InvariantCulture))
End Sub
End Module
The following example simplifies this code by instantiating the Func<T1,T2,T3,TResult> delegate instead of explicitly defining a new delegate and assigning a named method to it.
using System;
using System.Globalization;
public class GenericFunc
{
public static void Main()
{
string numericString = "-1,234";
Func<string, NumberStyles, IFormatProvider, int> parser = int.Parse;
Console.WriteLine(parser(numericString,
NumberStyles.Integer | NumberStyles.AllowThousands,
CultureInfo.InvariantCulture));
}
}
open System
open System.Globalization
let parseInt (str: string) styles format = Int32.Parse(str, styles, format)
let numericString = "-1,234"
let parser =
Func<string, NumberStyles, IFormatProvider, int> parseInt
parser.Invoke(
numericString,
NumberStyles.Integer ||| NumberStyles.AllowThousands,
CultureInfo.InvariantCulture )
|> printfn "%i"
Imports System.Globalization
Module GenericFunc
Public Sub Main()
Dim numericString As String = "-1,234"
Dim parser As Func(Of String, NumberStyles, IFormatProvider, Integer) _
= AddressOf Integer.Parse
Console.WriteLine(parser(numericString, _
NumberStyles.Integer Or NumberStyles.AllowThousands, _
CultureInfo.InvariantCulture))
End Sub
End Module
You can use the Func<T1,T2,T3,TResult> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods.)
using System;
using System.Globalization;
public class Anonymous
{
public static void Main()
{
string numericString = "-1,234";
Func<string, NumberStyles, IFormatProvider, int> parser =
delegate(string s, NumberStyles sty, IFormatProvider p)
{ return int.Parse(s, sty, p); };
Console.WriteLine(parser(numericString,
NumberStyles.Integer | NumberStyles.AllowThousands,
CultureInfo.InvariantCulture));
}
}
You can also assign a lambda expression to a Func<T1,T2,T3,TResult> delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (VB), Lambda Expressions (C#) and Lambda Expressions (F#).)
using System;
using System.Globalization;
public class LambdaExpression
{
public static void Main()
{
string numericString = "-1,234";
Func<string, NumberStyles, IFormatProvider, int> parser = (s, sty, p)
=> int.Parse(s, sty, p);
Console.WriteLine(parser(numericString,
NumberStyles.Integer | NumberStyles.AllowThousands,
CultureInfo.InvariantCulture));
}
}
open System
open System.Globalization
let numericString = "-1,234"
let parser = Func<string, NumberStyles, IFormatProvider, int>(fun s sty p ->
Int32.Parse(s, sty, p))
parser.Invoke(numericString,
NumberStyles.Integer ||| NumberStyles.AllowThousands,
CultureInfo.InvariantCulture)
|> printfn "%i"
Imports System.Globalization
Module LambdaExpression
Public Sub Main()
Dim numericString As String = "-1,234"
Dim parser As Func(Of String, NumberStyles, IFormatProvider, Integer) _
= Function(s, sty, p) Integer.Parse(s, sty, p)
Console.WriteLine(parser(numericString, _
NumberStyles.Integer Or NumberStyles.AllowThousands, _
CultureInfo.InvariantCulture))
End Sub
End Module
The underlying type of a lambda expression is one of the generic Func
delegates. This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. In particular, because many methods of types in the System.Linq namespace have Func
parameters, you can pass these methods a lambda expression without explicitly instantiating a Func
delegate.
Get |
Gets an object that represents the method represented by the specified delegate. |
Продукт | Версии |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
UWP | 10.0 |
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