Variables

Use var to declare a local variable:

var attempts: Int = 0;
var host: String = "127.0.0.1";

A variable may be assigned again:

var status = "waiting";
status = "ready";

The new value must have a compatible type. A variable’s type does not change after its declaration.

Immutable bindings

Use let for a local binding that cannot be assigned again. Like var, it accepts either an inferred or explicit type and always has an initializer:

let host = "127.0.0.1";
let port: Int = 8080;

The binding is immutable, not the object it refers to. A let binding can call methods that change the referenced object:

let names = new List<String>();
names.push("Ada");
println(names.front());

Use let when the name should keep the same value, and var when the binding itself must be assigned again.

Type inference

The compiler can infer a variable’s type from its initializer:

var port = 8080;
var ready = true;
var language = "Zap";

An explicit type is useful when the intended type differs from the literal’s default or when it makes an API boundary clearer:

var status: Int32 = 200;
var ratio: Float64 = 0.75;

Initialization and assignment

A declaration introduces a name:

var count = 1;

An assignment changes the value of an existing variable:

count = count + 1;

Using an unknown name or assigning an incompatible value is a compile-time error.

Scope

A variable is visible from its declaration to the end of the enclosing block:

fun choose(enabled: Bool) String {
    if enabled {
        var result = "enabled";
        return result;
    }

    return "disabled";
}

result is not visible outside the if block.

Continue with primitive types.