IPermission.IsSubsetOf Method (IPermission)


Determines whether the current permission is a subset of the specified permission.

Namespace:   System.Security
Assembly:  mscorlib (in mscorlib.dll)

Function IsSubsetOf (
	target As IPermission
) As Boolean


Type: System.Security.IPermission

A permission that is to be tested for the subset relationship. This permission must be of the same type as the current permission.

Return Value

Type: System.Boolean

true if the current permission is a subset of the specified permission; otherwise, false.

Exception Condition

The target parameter is not null and is not of the same type as the current permission.

The current permission is a subset of the specified permission if the current permission specifies a set of operations that is wholly contained by the specified permission. For example, a permission that represents access to C:\example.txt is a subset of a permission that represents access to C:\. If this method returns true, the current permission represents no more access to the protected resource than does the specified permission.

The following statements are required to be true for all implementations of the IsSubsetOf method. X, Y, and Z represent IPermission objects that are not null.

  • X.IsSubsetOf(X) returns true.

  • X.IsSubsetOf(Y) returns the same value as Y.IsSubsetOf(X) if and only if X and Y represent the same set of permissions.

  • If X.IsSubsetOf(Y) and Y.IsSubsetOf(Z) both return true, X.IsSubsetOf(Z) returns true.

If X represents an empty IPermission object with a permission state of None and Y represents an IPermission object that is null, X.IsSubsetOf(Y) returns true. If Z is also an empty permission, the compound set operation X.Union(Z).IsSubsetOf(Y) also returns true because the union of two empty permissions is an empty permission.

The following code example demonstrates implementing the IsSubsetOf method. This code example is part of a larger example provided for the IPermission class.

' Called by the Demand method: returns true if 'this' is a subset of 'target'.
Public Overrides Function IsSubsetOf(ByVal target As IPermission) As [Boolean]
    ' If 'target' is null and this permission allows nothing, return true.
    If target Is Nothing Then
        Return m_flags = 0
    End If
    ' Both objects must be the same type.
    Dim soundPerm As SoundPermission = VerifyTypeMatch(target)

    ' Return true if the permissions of 'this' is a subset of 'target'.
    Return m_flags <= soundPerm.m_flags

End Function 'IsSubsetOf

.NET Framework
Available since 1.1
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