Variables

Overview

A variable in MScript is declared as follows:

foo = "bar"

Type safety

MScript is a type-safe language, which means that for the duration of its scope and any child scopes, the name foo must always be a string.

foo = "bar"
foo = 5

 --> ./variables.ms:2:7
  |
2 | foo = 5
  |       ^
  |
  = type mismatch: this assignment will update a variable with type `int`, which is not compatible with the original type `str`
Error: Did not compile successfully (1 Error)

Generally, MScript can infer the type of an assignment based on the type of the to-be-assigned value. However, you may explicitly define a type as follows:

planets: int = 8
name: str = "Tom"

# this is okay! we're sticking with the same types
planets = 9
name = "Jerry"

Assignment modifiers

const

This modifier ensures that a variable will never be reassigned somewhere else in code.

const name = "Bard"
name = "zzzz"

 --> ./try_to_crash.ms:2:8
  |
2 | name = "zzzz"
  |        ^----^
  |
  = attempting to reassign to a const variable
Error: Did not compile successfully (1 Error)

It does not freeze the contents of a mutable object, like a list or class.

const list: [int...] = [1, 2, 3]
list.push(4)
list[0] = 10

assert list == [10, 2, 3, 4]

export

This modifier includes this variable in the file's module and makes it accessible from other .ms files. An assignment that is "exported" must explicitly define a type.

• This variable can be modified anywhere; be careful what you expose:

  export version: str = "v1.0.0"

• This variable can be read and copied anywhere, but not modifed:

  export const version: str = "v1.0.0"

modify

This modifier is used to update a variable visible to a function, but not in its immediate scope. The keyword is complex in nature, and likely used scarcely in real code. See the section about closures and captured variables for a more detailed breakdown of how this keyword operates.