Contract.ForAll<T> Method (IEnumerable<T>, Predicate<T>)
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Determines whether all the elements in a collection exist within a function.
Namespace: System.Diagnostics.Contracts
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Shared Function ForAll(Of T) ( _
collection As IEnumerable(Of T), _
predicate As Predicate(Of T) _
) As Boolean
public static bool ForAll<T>(
IEnumerable<T> collection,
Predicate<T> predicate
)
Type Parameters
- T
The type that is contained in collection.
Parameters
- collection
Type: System.Collections.Generic.IEnumerable<T>
The collection from which elements of type T will be drawn to pass to predicate.
- predicate
Type: System.Predicate<T>
The function to evaluate for the existence of all the elements in collection.
Return Value
Type: System.Boolean
true if and only if predicate returns true for all elements of type T in collection.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | collection or predicate is nulla null reference (Nothing in Visual Basic). |
Examples
The following example demonstrates how to use the ForAll method to determine whether a collection has a null element.
Imports System
Imports System.Diagnostics.Contracts
Imports System.Collections.Generic
Class Program
' Start application with at least two arguments.
Shared Sub Main(ByVal args() As String)
args(1) = Nothing
Contract.Requires(Not (args Is Nothing) AndAlso Contract.ForAll(args, Function(s) s Is Nothing))
' test the ForAll method. This is only for purpose of demonstrating how ForAll works.
CheckIndexes(args)
Dim numbers As New Stack(Of String)
numbers.Push("one")
numbers.Push("two")
numbers.Push("three")
numbers.Push("four")
numbers.Push("five")
Contract.Requires(Not (numbers Is Nothing) AndAlso Not Contract.ForAll(numbers, Function(s) s Is Nothing))
' test the ForAll generic overload. This is only for purpose of demonstrating how ForAll works.
CheckTypeArray(numbers)
End Sub 'Main
Private Shared Function CheckIndexes(ByVal args() As String) As Boolean
Try
If Not (args Is Nothing) AndAlso Not Contract.ForAll(0, args.Length, Function(i) args(i) Is Nothing) Then
Throw New ArgumentException("The parameter array has a null element", "args")
End If
Return True
Catch e As ArgumentException
Console.WriteLine(e.Message)
Return False
End Try
End Function 'CheckIndexes
Private Shared Function CheckTypeArray(ByVal xs As Stack(Of String)) As Boolean
Try
If Not (xs Is Nothing) AndAlso Not Contract.ForAll(xs, Function(s) s Is Nothing) Then
Throw New ArgumentException("The parameter array has a null element", "Stack")
End If
Return True
Catch e As ArgumentException
Console.WriteLine(e.Message)
Return False
End Try
End Function 'CheckTypeArray
End Class 'Program
using System;
using System.Diagnostics.Contracts;
using System.Collections.Generic;
namespace AssumeEx
{
class Program
{
// Start application with at least two arguments
static void Main(string[] args)
{
args[1] = null;
Contract.Requires(args != null && Contract.ForAll(0, args.Length, i => args[i] != null));
// test the ForAll method. This is only for purpose of demonstrating how ForAll works.
CheckIndexes(args);
Stack<string> numbers = new Stack<string>();
numbers.Push("one");
numbers.Push("two");
numbers.Push(null);
numbers.Push("four");
numbers.Push("five");
Contract.Requires(numbers != null && !Contract.ForAll(numbers, (String x) => x != null));
// test the ForAll generic overload. This is only for purpose of demonstrating how ForAll works.
CheckTypeArray(numbers);
}
private static bool CheckIndexes(string[] args)
{
try
{
if (args != null && !Contract.ForAll(0, args.Length, i => args[i] != null))
throw new ArgumentException("The parameter array has a null element", "args");
return true;
}
catch (ArgumentException e)
{
Console.WriteLine(e.Message);
return false;
}
}
private static bool CheckTypeArray(IEnumerable<String> xs)
{
try
{
if (xs != null && !Contract.ForAll(xs, (String x) => x != null))
throw new ArgumentException("The parameter array has a null element", "indexes");
return true;
}
catch (ArgumentException e)
{
Console.WriteLine(e.Message);
return false;
}
}
}
}
Version Information
Silverlight
Supported in: 5, 4
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.