References

They simply point to things...

A reference is a managed pointer to an existing variable. It acts as an alias. A reference is a variable in itself but does not carry its own value. It can read from as well as write to the original variable.

You can create a reference using the

symbol.

var name = "Kal".
var lang = &name. ;; ref to name

ref.kal

Here,

name

is the original variable which holds an actual value.

lang

on the other hand is a reference that refers/points to name.

lang

itself does not have its own value.

Also note that, lang directly points to “Kal”, it does not copy the value. Since a reference is not a copy, it occupies very little space in the memory.

You can have multiple references to an existing variable. Modifying the reference also modifies the original value.

var count = 0.
stdout "Count = " count "\n".

var countRef = &count.
countRef = 10.

stdout "Count = " count "\n".

ref.kal

You can have references to elements of lists and dictionaries as well.

var data = [1, 2, 3].
var item = &data[1].
item = item * 10.
stdout data "\n".

ref.kal

You must be very careful when creating references as any unintended change to the reference will change the base variable.

When you pass a variable to a function, it treats it as a value and makes a copy. This is where references can be useful.

You may not want to pass data as value for two main reasons:

Modify the data via the function.
Avoid making extra copies.

Passing by reference addresses both of these reasons.

Let's look at an example:

fn change -> x {
    x = x * 10.
    stdout "In Fn: " x "\n".
}

var data = 5.
stdout "Before: " data "\n".
:change data.
stdout "After: " data "\n".

passByRefBuggy.kal

That's weird, right?

data

should have changed but it didn't. Well, here's what happened:
When

data

was passed to the function

change

, the function made a copy of it and assigned it to

, therefore

changed, but

data

never did. The change was visible only inside the function.

To make this example code work, simply pass

data

to change by reference as

&data

fn change -> x {
    x = x * 10.
    stdout "In Fn: " x "\n".
}

var data = 5.
stdout "Before: " data "\n".
:change &data. ;; passed by reference
stdout "After: " data "\n".

passByRef.kal

References can be passed during the function invocation. They do not need to be declared in any way during function definition.

Similarly, you can also loop over an array by reference:

var data = [1, 2, 3].
stdout "Before: " data "\n".

loop &each in data {
    each = each * 10.
}

stdout "After: " data "\n".

loopByRef.kal

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