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Variables¶

To create a variable, you need to use the let keyword:

1	let myVariable = "Hello World!"

Note

Every variable in Pineapple must start with lowercase letter and cannot contain any spaces or underscore.
The following are invalid variable names:

let Message = "Yo" // Invalid, cannot start with uppercase letter

let my name = "Wong" // Invalid, cannot contain spaces

let my_pet = "Cat" // Invalid, cannot contain underscore

Type inference¶

The type of each variables are resolved automatically by the Pineapple compiler, so you don't need to provide any type annotation.
For example:

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let x = "yo"    // x has type of String
let y = 0       // y has type of Integer
let z = [1,2,3] // z has type of List{Integer}

Although unnessecary, it is also possible to annotate variables with type manually:

1	let x String = "yo"

Default immutability¶

By default, all variables in Pineapple are immutable, it means that you cannot assign a new value to it after you declare it.

1 2	let count = 0 count = 1 // Error

Info

Mutable means changeable.
Immutable means not changeable.

If you wish to make a variable mutable, you need to use the mutable keyword.

1 2	let mutable x = 0 x = 1 // No error

Tip

This feature is implemented on purpose to discourage programmers from mutating variables all the time.
So, instead of creating one variables and change it all the time, create as many variables as you want!

Default non-nullablility¶

By default, you cannot assign #nil to a mutable variable.

1 2	let mutable x = 0 x = #nil // Error

What is nil?

Nil is actually same as null, just that nil is easier to type, so nil is adapted in Pineapple.

If you want to assign #nil to a variable, you need to declare it explicitly by using nilable types (which is to add a question mark behind the type name).

1 2	let mutable x Int? = 0 x = #nil // No error

Pass by value¶

When you try to assign the value of one variable to another variable, the value is copied, instead of copying its reference.

For example,

let john = People
    :name = "John"
    :age  = 99

let newJohn = john // copy john to newJohn

newJohn:name = "Johnny Bravo"

john:name.show // Still "John"

Why?

This feature is to prevent programmer from facing crazy bugs caused by pass-by-reference.

Optimization (implementing)¶

Of course, pass-by-value is expensive, thus it might slows down the program performance.
Fortunately, the Pineapple compiler will use pass-by-reference whenever possible.

For example:

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let x = 10
let y = x // x's value is pass-by-reference since it is not used afterwards
y.show

Another example:

let x = 10
let y = x // x's value is pass-by-value, since it is still in used after this line
x.show
y.show