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Learning Exercise
A C# Attribute provides a way to decorate a declaration to associate metadata to: a class, a method, an enum, a field, a property or any other supported declarations.
You can apply an attribute by adding it on the line before the declaration using a ClassAttribute and a FieldAttribute:
[Class]
class MyClass
{
[Field]
int myField;
}
This declarative metadata only associates additional structured information to the code and does not modify its behavior, but that metadata is used by other part of the code to change how its target would behave or add, change or remove, restrict some its functionalities.
There are many predefined and reserved attributes, for example: Flags, Obsolete, Conditional, each has a specific that can be looked up on the C# documentation. Note that the full name of an attribute like Flags
The C# enum type represents a fixed set of named constants (an enumeration).
Normally, one enum member can only refer to exactly one of those named constants. However, sometimes it is useful to refer to more than one constant. To do so, one can annotate the enum with the Flags attribute
A flags enum can be defined as follows (using binary integer notation 0b):
[Flags]
enum PhoneFeatures
{
Call = 0b00000001,
Text = 0b00000010
}
A PhoneFeatures instance which value is 0b00000011 has both its Call and Text flags set.
By default, the int type is used for enum member values. One can use a different integer type by specifying the type in the enum declaration:
[Flags]
enum PhoneFeatures : byte
{
Call = 0b00000001,
Text = 0b00000010
}
In this exercise you'll be checking permissions of user accounts on an internet forum. The forum supports three different permissions:
There are three types of accounts, each with different default permissions:
Sometimes individual permissions can be modified, it is possible for example to give a guest account the permission to also write posts or revoking all permissions from an account would result in having none of the permissions.
First, define an AccountType enum to represent the three account types: Guest, User and Moderator.
Next, define a Permission enum to represent the three permission types: Read, Write, Delete, and two extra ones: All for having all permissions and None for having none of the permissions.
Then implement the (static) Permissions.Default() method to return the default permissions for a specific account type:
Permissions.Default(AccountType.Guest)
// => Permission.Read
Implement the (static) Permissions.Grant() method that grants (adds) a permission:
Permissions.Grant(current: Permission.None, grant: Permission.Read)
// => Permission.Read
Implement the (static) Permissions.Revoke() method that revokes (removes) a permission:
Permissions.Revoke(current: Permission.Read, revoke: Permission.Read)
// => Permission.None
Implement the (static) Permissions.Check() method that takes the current account's permissions and checks if the account is authorized for a given permission:
Permissions.Check(current: Permission.Write, check: Permission.Read)
// => false
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