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, an integer is never implicitly convertible to a scoped enumeration type instance, this one 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 the many lacks of FreeBASIC on the normal Enum features.

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
Back to Programmer's Guide
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