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dotnetnoob
dotnetnoob

Reputation: 11330

Do enums need an index?

I have a number of enums that contain long lists that do change from time to time

public MyEnumType MyEnum
{
    None = 0,
    Option1 = 1,
    Option2 = 2,
    etc..
}

When they change, I need to renumber the index as invariably new options are placed inbetween existing options.

The question is, if I remove the index, will the enum always honour the order from top to bottom?

public MyEnumType MyEnum
{
    None,
    Option1,
    Option2,
    etc..
}

Thanks in advance.

Upvotes: 1

Views: 169

Answers (5)

Buh Buh
Buh Buh

Reputation: 7546

By default they will count up from zero in the order they are declared.
If you define one explicitly, then the subsequent values continue counting up, using the explicit value as a seed.

Upvotes: 1

Parag Meshram
Parag Meshram

Reputation: 8511

Simplest answer would be "Yes"... they will always honor the order.

So you no need to put index number.

public MyEnumType MyEnum
{
    None,
    OptionA,
    OptionB,
    OptionC,
    ...
    ...
    OptionZ
}

this will always same as -

public MyEnumType MyEnum
{
    None = 0,
    OptionA = 1,
    OptionB = 2,
    OptionC = 3,
    ...
    ...
    OptionZ = 26
}

If you introduce new enum type in between like -

public MyEnumType MyEnum
{
    None,
    OptionA,
    OptionB,
    OptionC,
    ...
    ...
    OptionO
    OptionNew
    OptionP
    ...
    ...
    OptionZ
}

Then above will be equivalent to -

public MyEnumType MyEnum
{
    None = 0,
    OptionA = 1,
    OptionB = 2,
    OptionC = 3,
    ...
    ...
    OptionO = 15
    OptionNew = 16
    OptionP = 17
    ...
    ...
    OptionZ = 27
}

Upvotes: 3

Tim Schmelter
Tim Schmelter

Reputation: 460138

From the C# language specification 1.10 Enums:

... When an enum member declaration does not explicitly specify a value, the member is given the value zero (if it is the first member in the enum type) or the value of the textually preceding enum member plus one.

So the same as your explicit declaration here:

public MyEnumType MyEnum
{
    None = 0,
    Option1 = 1,
    Option2 = 2,
    etc..
}

Upvotes: 1

slugster
slugster

Reputation: 49984

Yes they honour the order, starting from the default value for int, which is zero.

If you are regularly renumbering things then it is better to explicitly assign values to the enum members, and then re-number the items when the underlying list that it is based on changes.

If you use explicit numbering then you can also insert new items into the list between existing items at any time, although you do need to be careful that you don't assign two items to the same value (which is totally legal in C#, but may produce errors if you didn't intend it).

Upvotes: 1

Zdeslav Vojkovic
Zdeslav Vojkovic

Reputation: 14591

Yes they will. You can also specify just the first element if you want to make sure that values start at some specific value:

public MyEnumType MyEnum
{
    None = 1,
    Option1, // -> 2
    Option2, // -> 3
}

For other details, check the docs.

Note that in most scenarios, your code should not care about the exact numeric values. Situations when you do care are e.g. if you declare an enum which is an alias for an external type (e.g interop) so you need to ensure that values are the same. Another scenario is when the enumeration represents binary flags, then you want something like:

[Flags] 
public MyEnumType MyEnum
{
    None = 1,
    Option1 = 2,
    Option2 = 4
}

Upvotes: 6

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