2.20. Constants, Enumerations, Global variables

Daslang allows you to bind constant values to a global variable identifier. Whenever possible, all constant global variables will be evaluated at compile time. There are also enumerations, which are strongly typed constant collections similar to enum classes in C++.

2.20.1. Constant

Constants bind a specific value to an identifier. Constants are exactly global variables. Their value cannot be changed.

Constants are declared with the following syntax:

  foobar = 100
  floatbar = 1.2
  stringbar = "I'm a constant string"
let blah = "I'm string constant which is declared on the same line as variable"

Constants are always globally scoped from the moment they are declared. Any subsequential code can reference them.

You can not change such global variables.

Constants can be shared:

let shared blah <- [{string "blah"; "blahh"; "blahh"}]

Shared constants point to the same memory in different instances of Context. They are initialized once during the first context initialization.

2.20.2. Global variable

Mutable global variables are defined as:

  foobar = 100
var barfoo = 100

Their usage can be switched on and off on a per-project basis via CodeOfPolicies.

Local static variables can be declared via the static_let macro:

require daslib/static_let

def foo
    static_let <|
        var bar = 13
    bar = 14

Variable bar in the example above is effectively a global variable. However, it’s only visible inside the scope of the corresponding static_let macro.

Global variables can be private or public

let public foobar = 100

let private barfoo = 100

If not specified, structures inherit module publicity (i.e. in public modules global variables are public, and in private modules global variables are private).

2.20.3. Enumeration

An enumeration binds a specific value to a name. Enumerations are also evaluated at compile time and their value cannot be changed.

An enum declaration introduces a new enumeration to the program. Enumeration values can only be compile time constant expressions. It is not required to assign specific value to enum:

enum Numbers
    zero     // will be 0
    one      // will be 1
    two      // will be 2
    ten = 9+1 // will be 10, since its explicitly specified

Enumerations can be private or public:

enum private Foo

enum public Bar

If not specified, enumeration inherit module publicity (i.e. in public modules enumerations are public, and in private modules enumerations are private).

An enum name itself is a strong type, and all enum values are of this type. An enum value can be addressed as ‘enum name’ followed by exact enumeration

let one: Numbers = Numbers one

An enum value can be converted to an integer type with an explicit cast

let one: Numbers = Numbers one
assert(int(one) == 1)

Enumerations can specify one of the following storage types: int, int8, int16, uint, uint8, or uint16:

enum Characters : uint8
    ch_a = 'A'
    ch_b = 'B'

Enumeration values will be truncated down to the storage type.

The each_enum iterator iterates over specific enumeration type values. Any enum element needs to be provided to specify the enumeration type:

for x in each_enum(Characters ch_a)
        print("x = {x}\n")