Back to overview

6. Variables and Assignment

6.1 Declaring variables with :=

Each variable needs to be declared and initialized with :=:

x := 3
name := "Alice"
count := false

Variable values can later be modified using the = operator.

This syntax is useful when we want to explicitly initialize a variable upon creation. However, inside functions, we can also use a type annotation to declare a variable. In that case, the variable is given a default initial value.

a: int
s1: String
nums: Vec[int]
people: Dict[Vec[Person]]

Defaults per type are:

• Integers: 0
• Doubles: 0.0
• Booleans: false
• Characters: 0
• Strings ""
• Structs: struct with each field default initialized
• Vectors: empty vector of given type
• Dictionaries: empty dict of given type
• Variants: variant with active payload default initialized

At top level, globals are declared with :=. Typed declarations such as x: int are for local variables inside functions.

6.2 Local scope and redeclaration rules

Local variables live in block scopes, but Jik does not currently allow C-style shadowing.

In practice:

• a local name may not be redeclared in an inner block if it already exists in an outer local scope of the same function
• parameters and loop variables follow the same rule
• a local variable also may not shadow a global declared in the same module

So code such as the following is a compile error:

value := 1

func main(flag: bool):
    if flag:
        value := 2   // not allowed
    end
end

6.3 Binding immutability and object mutability

Immutability of a binding does not make a composite value deeply immutable. These are two different operations:

• assignment replaces the value held by a binding
• mutation changes an existing composite object through a field, vector element, or dictionary entry

Global bindings are initialized once and cannot be reassigned. If a global holds a mutable composite value, however, that object's contents can still be changed:

struct Box:
    value: int
end

global_box := Box{value=1}

func main():
    // global_box = Box{value=2} // invalid: the global binding cannot be replaced
    global_box.value = 2        // valid: the existing Box is mutated
end