> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # Dart For Loop A `for` loop in Dart is a control flow statement used to execute a block of code repeatedly based on a boolean condition, or to iterate over the elements of an `Iterable` or `Stream`. Dart provides three primary syntactical constructs for iteration: the traditional C-style `for` loop, the `for-in` loop for synchronous collections, and the asynchronous `await for` loop for streams. ## Standard `for` Loop The standard `for` loop relies on an explicit loop counter and consists of three optional expressions: initialization, condition, and update. ```dart theme={"dark"} for (var i = 0; i < 5; i++) { print(i); } ``` * **Initialization:** Executed exactly once before the loop begins. Variables declared here are lexically scoped to the loop block. * **Condition:** Evaluated before each iteration. If it resolves to `true`, the execution block runs. If `false`, the loop terminates. * **Update:** Executed at the end of each iteration, typically used to mutate the loop counter. **Closure Capture Mechanics:** Dart captures the state of the loop variable inside closures correctly. Each iteration of the loop creates a new lexical scope for the loop variable, meaning asynchronous callbacks or closures defined within the loop will capture the exact value of the variable for that specific iteration, rather than a reference to the final mutated variable. ```dart theme={"dark"} var callbacks = []; for (var i = 0; i < 3; i++) { callbacks.add(() => print(i)); // Captures 0, 1, 2 respectively } ``` ## `for-in` Loop The `for-in` loop is a declarative construct used to traverse objects that implement the `Iterable` interface (such as `List` or `Set`). It abstracts away the underlying `Iterator` mechanics (`moveNext()` and `current`). ```dart theme={"dark"} var numbers = [1, 2, 3]; for (var number in numbers) { print(number); } ``` **Pattern Matching (Dart 3.0+):** The `for-in` loop supports Dart's pattern matching and destructuring. If the `Iterable` contains structured data like Records or instances of a class, they can be destructured directly in the loop declaration. ```dart theme={"dark"} var coordinates = [(1, 2), (3, 4), (5, 6)]; for (var (x, y) in coordinates) { print('X: $x, Y: $y'); } ``` ## Asynchronous `await for` Loop The `await for` loop is an asynchronous control flow construct used to consume elements from a `Stream`. It suspends execution of the surrounding `async` function until the stream emits a new event, executing the loop body for each data event and terminating when the stream is closed. ```dart theme={"dark"} Future processStream(Stream numberStream) async { await for (var number in numberStream) { print(number); } } ``` ## Control Transfer Statements Dart provides keywords to alter the standard execution flow within any `for` loop: * `break`: Immediately terminates the innermost enclosing loop. * `continue`: Bypasses the remaining statements in the current execution block. In a standard `for` loop, it jumps directly to the **update** expression. In a `for-in` or `await for` loop, it advances to the next element. **Labeled Statements:** For nested loops, Dart supports labels to direct `break` or `continue` statements to a specific loop level. ```dart theme={"dark"} void processMatrix() { outerLoop: for (var i = 0; i < 5; i++) { for (var j = 0; j < 5; j++) { if (i == 2 && j == 2) { break outerLoop; // Terminates both loops } } } } ``` ## The `forEach` Method While technically a higher-order method rather than a loop statement, `forEach` is a functional alternative available on all `Iterable` objects. It accepts a callback function and applies it to every element. ```dart theme={"dark"} var items = ['A', 'B', 'C']; items.forEach((element) { print(element); }); ``` *Note:* Control transfer statements (`break` and `continue`) cannot be used inside the `forEach` callback, as the block is a separate function scope, not a loop body. To terminate iteration early, a standard `for` or `for-in` loop must be used.

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