for Loops

VDX supports two styles of for loop: C-style and for-in (array/string/dict iteration).

⚠️ Loop Protection

Both C-style for loops and for-in loops are subject to the same loop safety protection as while loops. Use @unsafe for fast loops.

C-style for loop

for (init; condition; update) {
    // body
}

class App {
    @unsafe for (let i = 0; i < 5; i = i + 1) {
        print("i:", i);
    }
    // Output: i: 0, i: 1, i: 2, i: 3, i: 4
}

The init part can use let to declare a new variable, or assign to an existing one. The update part is any assignment or increment/decrement — i++, arr[i] = v, obj.n-- all work (v0.1.5+; no semicolon needed).

for-in loop

Iterate over an array (elements), a string (characters, v0.1.5+), or a dict (keys in sorted order, v0.1.5+):

for (variable in iterable) {
    // body — variable holds the current element / char / key
}

class App {
    let fruits = ["apple", "banana", "cherry"];
    for (fruit in fruits) {
        print("fruit:", fruit);
    }

    for (ch in "hi") {          // v0.1.5+ — h, i
        print("char:", ch);
    }

    let d = {"b": 2, "a": 1};
    for (k in d) {              // v0.1.5+ — keys sorted: a, b
        print(k, "=", d[k]);
    }
}

For-in loops are also subject to loop safety protection — halted if an iteration takes more than 2s of work or the loop exceeds 1,000,000 iterations (v0.1.5+). Use @unsafe to bypass.

Accumulating with for

class App {
    let sum: float = 0.0;
    let values = [1.5, 2.5, 3.0];
    for (v in values) {
        sum = sum + v;
    }
    print("sum:", sum);   // sum: 7.0
}

Nested for loops

class App {
    @unsafe for (let i = 0; i < 3; i = i + 1) {
        @unsafe for (let j = 0; j < 3; j = j + 1) {
            print(i, j);
        }
    }
}

Scoping

The loop variable in a C-style for is scoped to the loop. In a for-in loop, the iteration variable is scoped to each iteration. See Scoping Rules.