Combining enum values

Daily Knowledge Drop

The bitwise logical operator (|) can be used to combine enum values when assigning to a variable, but they can also be used when defining the enum to create enum values which are a combination of other enum values.

Combine variable

This is the more common (in my experience) usage of combining enums - assigning enum value(s) to a variable.

Consider the following enum:

[Flags]
enum OrderStatus
{
    New = 1,
    Processing = 2,
    Reserved = 4,
    Paid = 8,
    Delivered = 16,
    Cancelled = 32
}

We could indicate that an order is Paid but also been Cancelled by doing the follow:

OrderStatus status = OrderStatus.Paid | OrderStatus.Cancelled;

Console.WriteLine($"Is order Paid? {status.HasFlag(OrderStatus.Paid)}");
Console.WriteLine($"Is order Cancelled? {status.HasFlag(OrderStatus.Cancelled)}");

With the output being:

Is order Paid? True
Is order Cancelled? True

The bitwise logical operator (|) can also be used when declaring the enum to combine statues.

Combine declaration

Consider the same enum from above:

[Flags]
enum OrderStatus
{
    New = 1,
    Processing = 2,
    Reserved = 4,
    Paid = 8,
    Delivered = 16,
    Cancelled = 32
}

Suppose we wanted two methods to determine if a order is currently Open (still processing to do) or if it is Closed (no more processing to do).

With the enums as they are, something similar to this would need to be done:

// check all the statuses considered 'open'
bool IsOrderOpen(OrderStatus status) => status.HasFlag(OrderStatus.New) ||
        status.HasFlag(OrderStatus.Processing) ||
        status.HasFlag(OrderStatus.Reserved) ||
        status.HasFlag(OrderStatus.Paid);

// check all the statuses considered 'closed'
bool IsOrderClosed(OrderStatus status) => status.HasFlag(OrderStatus.Delivered) ||
        status.HasFlag(OrderStatus.Cancelled);

Each time a new status is added and the enum changes, the developer would need to remember to come in and update each method as well.

A cleaner approach, is to define a new status, and use it to combine with other statuses.

Consider this updated enum:

[Flags]
enum OrderStatus
{
    New = 1 | 64,
    Processing = 2 | 64,
    Reserved = 4 | 64,
    Paid = 8 | 64,
    Delivered = 16 | 128,
    Cancelled = 32 | 128,
    Open = 64,
    Closed = 128
}

Two new statuses, Open and Closed, have been defined, with each other status being updated to indicate it as being either Open or Closed. For example Processing = 2 | 64, effectively means: an order with a status of Processing is Processing but also Open.

To check if an order is Open or Closed now, all that is required is the following:

bool IsOrderOpen(OrderStatus status) => status.HasFlag(OrderStatus.Open);
bool IsOrderClosed(OrderStatus status) => status.HasFlag(OrderStatus.Closed);

Using the methods:

// the status is not set explicitly to 'Open' or 'Closed'
var status = OrderStatus.Reserved;

Console.WriteLine($"Is order open? {IsOrderOpen(status)}");
Console.WriteLine($"Is order closed? {IsOrderClosed(status)}");

// just to confirm a check on the original status 
// still works
Console.WriteLine($"Is order reserved? {status.HasFlag(OrderStatus.Reserved)}");

The output:

Is order open? True
Is order closed? False
Is order reserved? True

This version of the code is definitely much cleaner, and much easier to maintain!

Notes

Using the bitwise logical operator (|) on enum definition is a useful technique I was not aware of. It facilities cleaner code, and makes it easier for the developer to contain enum logic all in one place.

References

Enum bit-shifting syntax for multiple flags during enum declaration

Daily Drop 141: 18-08-2022

At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.

The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.