Variables and Bindings

Declarations bind names to values. There are three binding declarations: const, val, and var.

const MaxRetries = 3;
val limit = MaxRetries * 2;
var attempts = 0;
attempts = attempts + 1;
print(MaxRetries, limit, attempts);

3 6 1

• const declares a compile-time constant: the value must be computable at compile time and cannot be reassigned afterwards. Use it for the limits, thresholds, and configuration numbers baked into the program;
• val declares an immutable binding: limit is 6 from now on and cannot change;
• var declares a mutable variable: attempts went from 0 to 1.

Like val, const refuses reassignment:

MaxRetries = 4;   // ✗ a const name cannot be reassigned

var has one more trick its two siblings lack: declare first, assign later (the type must be written out):

var counter: int;
counter = 0;
counter += 10;
print(counter);

10

Compile-time evaluation of const

A const initial value is evaluated and folded at compile time: literal arithmetic (6 * 7), references to other consts, and whitelisted Math functions from the standard library may all appear in a const position, and the result is baked straight into the compiled output:

const ConstFolded: int = Math.Clamp(80 * 2, 0, 100);
print(ConstFolded);

100

What may appear in a const position has clear bounds; for more elaborate compile-time computation, use a const func (see const funcs).

Destructuring declarations

val / var also support a destructuring form: a pattern on the left declares several names at once. Vectors and tuples can both be unpacked:

val (x, y) = vec2i(3, 4);
print(x, y);

3 4

Destructuring is just declaration-position syntax; the patterns themselves belong to the pattern system, whose full set is covered on the patterns page.

Notes

• Names for all three bindings follow the identifier rules and are case-sensitive.
• A const initial value is evaluated at compile time and limited to what that position allows; see const funcs for details.
• Binding types are usually inferred; when inference fails, write the type after the colon (like counter: int above).