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Constants and Enumerations

Documentation

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