Bob Nystrom
6ed15da597
Add `^category` front matter to all language, types, and reference doc pages for site navigation restructuring. Replace `:::wren` and `:::java` code block annotations with `:::dart` across multiple files. Create new stub pages for core-libraries, embedding-api, and contributing under the reference category. Remove the old embedding and getting-involved stub pages.
1.8 KiB
^title Variables ^category language
Variables are named slots for storing values. You can define a new variable in
Wren using a var statement, like so:
:::dart
var a = 1 + 2
This creates a new variable a in the current scope and initializes it with
the result of the expression following the =. Once a variable has been
defined, it can be accessed by name as you would expect.
:::dart
var animal = "Slow Loris"
IO.print(animal) // Prints "Slow Loris".
Scope
Wren has true block scope: a variable exists from the point where it is defined until the end of the block where that definition appears.
:::dart
{
IO.print(a) // ERROR! a doesn't exist yet.
var a = 123
IO.print(a) // "123"
}
IO.print(a) // ERROR! a doesn't exist anymore.
Variables defined at the top level of a script are global. All other variables are local. Declaring a variable in an inner scope with the same name as an outer one is called shadowing and is not an error (although it's not something you likely intend to do much).
:::dart
var a = "outer"
{
var a = "inner"
IO.print(a) // Prints "inner".
}
IO.print(a) // Prints "outer".
Declaring a variable with the same name in the same scope is an error.
:::dart
var a = "hi"
var a = "again" // ERROR!
Assignment
After a variable has been declared, you can assign to it using =:
:::dart
var a = 123
a = 234
An assignment walks up the scope stack to find where the named variable is declared. It's an error to assign to a variable that isn't defined. Wren doesn't roll with implicit variable definition.
When used in a larger expression, an assignment expression evaluates to the assigned value.
:::dart
var a = "before"
IO.print(a = "after") // Prints "after".
TODO: Forward references for globals, closures.