Constants and Enumerations
Enumeration, a special User-Defined Type composed of a number of named constants.
Syntax
`Enum [typename [ Explicit ] ]
symbolname [= expression] [, ...]
...
End Enum`
Parameters
`typename`
Name of the `Enum`
`symbolname`
Name of the constant
`expression`
A constant expression
`Explicit`
Requires that symbols must be explicitly referred to by `typename.symbolname`
Description
An enumeration is a User-Defined Type that consists of a set of named integer constants.
Enumerations are useful for defining sequences and states, particularly when there is a natural progression through those states.
An enumeration provides context to describe a range of values which are represented as named constants through symbols.
Unlike namespaces, enumerations can be also defined in any scope blocks, and their symbols are only visible throughout the scope in which the enumeration is declared.
Enumerations lend themselves to more maintainable code because they are symbolic, allowing you to work with integer values ​​while using an explicit name.
Enumerations are value Types, which means they contain their own value, can not inherit or be inherited from.
`Enum` can not contain any member procedure or member data (only symbols), but it can be included (named or unnamed) in a `Type` by having.
Usage
Every symbol in an enumeration is implicitly assigned an integer value (positive or negative) that corresponds to its place in the order of the values in the enumeration.
Every symbol is treated as a constant.
By default, the first value is assigned 0, the next one is assigned 1, and so on.
But you can explicitly set the value of any symbol (and the next symbol will be implicitly set to the previous value plus an increment of one).
The values given to the symbols do not have to be unique.
When an enumeration is qualified as `Explicit`, access to any `symbolname` must be always prefixed by `typename`.
Prefixing can also be used to solve ambiguity with other entities.
An `Enum` instance can be passed, as any User-Defined Type instance, to a procedure (including for the definition of overloaded operators).
The size of an `Enum` instance will be always that of an `Integer` (no matter how many defined symbols are just declarations for the compiler assignment).
An `Enum` instance (or `Enum` symbol) can be implicitly converted to an integer.
Note:
- In many languages, no integer variable is implicitly convertible into a scoped enumeration type instance (and vice versa), the latter being strongly typed (declaration equivalent to the `Enum` qualified as `Explicit` with FreeBASIC), and an explicit cast is required for such a conversion.
- But FreeBASIC accepts it (even if the numeric value does not match any `Enum` symbol defined). This is just one of FreeBASIC's many shortcomings over normal `Enum` functionality.
- Therefore, there is not much interest in declaring a real `ENUM` instance (which is sized as an INTEGER), but otherwise any pre-built integer variable can be declared instead.
- If the `Explicit` qualifier is not used (namespace prefix not imposed), there is not much point in using an `ENUM` structure compared to a simple discrete list of constants, except for the auto-increment of values.
Example
Simple example of use:
`
Enum Colors
black
blue
green
cyan
red
pink
yellow
grey
dark_grey
bright_blue
bright_green
bright_cyan
bright_red
bright_pink
bright_yellow
white
End Enum
Sub print_fbc (ByVal foreground As Colors, ByVal background As Colors)
Color foreground, background
Print " " & __FB_SIGNATURE__ & " "
End Sub
Dim As Colors std_foreground, std_background
std_foreground = LoWord(Color())
std_background = HiWord(Color())
Dim As Colors my_foreground, my_background
my_foreground = bright_yellow
my_background = cyan
print_fbc(my_foreground, my_background)
Color std_foreground, std_background
Print "end"
Sleep
`
Same result, but with a `Type` interfacing `Enum` to impose explicit casting when assigning numeric values to `Enum` instances (see 'Note' above):
`
Enum Colors Explicit
black
blue
green
cyan
red
pink
yellow
grey
dark_grey
bright_blue
bright_green
bright_cyan
bright_red
bright_pink
bright_yellow
white
End Enum
Type Console_Colors
Public:
Declare Property foreground () As Colors
Declare Property foreground (ByVal c As Colors)
Declare Property background () As Colors
Declare Property background (ByVal c As Colors)
Private:
Dim As Colors _foreground
Dim As Colors _background
End Type
Property Console_Colors.foreground () As Colors
Return This._foreground
End Property
Property Console_Colors.foreground (ByVal c As Colors)
This._foreground = c
End Property
Property Console_Colors.background () As Colors
Return This._background
End Property
Property Console_Colors.background (ByVal c As Colors)
This._background = c
End Property
Sub print_fbc (ByVal foreground As Colors, ByVal background As Colors)
Color foreground, background
Print " " & __FB_SIGNATURE__ & " "
End Sub
Dim As Console_Colors std_colors
std_colors.foreground = Cast(Colors, LoWord(Color())) '' explicit cast mandatory because of property declaration
std_colors.background = Cast(Colors, HiWord(Color())) '' explicit cast mandatory because of property declaration
Dim As Console_Colors my_colors
my_colors.foreground = Colors.bright_yellow
my_colors.background = Colors.cyan
print_fbc(my_colors.foreground, my_colors.background)
Color std_colors.foreground, std_colors.background
Print "end"
Sleep
`
See also

- `Enum`
- `Type`
- Constants