3.11. Constants & Enumerations

Quirrel allows to bind constant values to an identifier that will be evaluated compile-time. This is achieved though constants and Enumerations.

3.11.1. Constants

Constants bind a specific value to an identifier. Constants are similar to global values, except that they are evaluated compile time and their value cannot be changed.

constants values can only be integers, floats or string literals. No expression are allowed. are declared with the following syntax.:

const foobar = 100
const floatbar = 1.2
const stringbar = "I'm a constant string"

Constants are locally scoped, from the moment they are declared. To make constant global, use the global keyword.:

global const baz = 123

Constants will shadow any global slot with the same name( the global slot will remain visible by using the :: syntax).:

let x = foobar * 2

3.11.2. Enumerations

As Constants, Enumerations bind 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 into the program. Enumeration values can only be integers, floats or string literals. No expression are allowed.:

enum Stuff {
  first, //this will be 0
  second, //this will be 1
  third //this will be 2
}

or:

enum Stuff {
  first = 10
  second = "string"
  third = 1.2
}

An enum value is accessed in a manner that’s similar to accessing a static class member. The name of the member must be qualified with the name of the enumeration, for example Stuff.second Enumerations will shadow any global slot with the same name( the global slot will remain visible by using the :: syntax).:

let x = Stuff.first * 2

Like with constants, to declare globally-scoped enum, use the global keyword.:

global enum Stuff { first, second }

3.11.3. Implementation notes

Enumerations and Constants are a compile-time feature. Only integers, string and floats can be declared as const/enum; No expressions are allowed (because they would have to be evaluated compile time).

If a const or enum is global, when declared it is added compile time to the consttable. This table is stored in the VM shared state and is shared by the VM and all its threads. The consttable is a regular quirrel table; In the same way as the roottable it can be modified runtime. You can access the consttable through the built-in function getconsttable() and also change it through the built-in function setconsttable()

here some example:

//creates a constant
getconsttable()["something"] <- 10"
//creates an enumeration
getconsttable()["somethingelse"] <- { a = "10", c = "20", d = "200"};
//deletes the constant
delete getconsttable()["something"]
//deletes the enumeration
delete getconsttable()["somethingelse"]

This system allows to procedurally declare constants and enumerations, it is also possible to assign any quirrel type to a constant/enumeration(function,classes etc…). However this will make serialization of a code chunk impossible.