> ## 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 Null-Aware Spread The `...?` (null-aware spread) operator evaluates an expression that yields a collection, and if that collection is not `null`, unpacks its elements into the surrounding collection literal. If the evaluated expression is `null`, the operator safely ignores it and performs no operation, preventing runtime null dereference exceptions. ## Syntax The operator is placed immediately preceding the nullable collection identifier or expression within a collection literal (List, Set, or Map). ```dart theme={"dark"} // For Lists and Sets (operates on Iterables) [elementA, ...?nullableIterable, elementB] {elementA, ...?nullableIterable, elementB} // For Maps (operates on Map entries) {keyA: valueA, ...?nullableMap, keyB: valueB} ``` ## Evaluation Mechanics When the Dart compiler encounters the `...?` operator, it executes the following logical sequence: 1. **Expression Evaluation:** It evaluates the operand to the right of the `...?` operator. 2. **Null Check:** It checks if the resulting value is `null`. 3. **Branching:** * **If `null`:** The operator acts as a no-op. No elements are yielded to the surrounding collection literal, and execution proceeds to the next element in the literal. * **If non-null:** The operator behaves identically to the standard spread operator (`...`). It requests an `Iterator` from the collection and sequentially appends each element (or key-value pair, in the case of a Map) into the surrounding collection literal. ## Code Visualization ```dart theme={"dark"} List? nullList; List? populatedList = [2, 3]; // The nullList is safely ignored. List resultA = [1, ...?nullList, 4]; // Evaluates to: [1, 4] // The populatedList is unpacked. List resultB = [1, ...?populatedList, 4]; // Evaluates to: [1, 2, 3, 4] ``` ## Type System Interaction Under Dart's sound null safety, the standard spread operator (`...`) requires an operand with a strictly non-nullable type (e.g., `List`). Attempting to use `...` on a nullable type (e.g., `List?`) results in a compile-time error. The `...?` operator explicitly signals to the analyzer that the potential `null` state is handled. It accepts operands of type `Iterable?` (for Lists/Sets) or `Map?` (for Maps). The surrounding collection literal infers its type based on the generic type parameters of the unpacked collection, stripping away the nullability of the collection itself.

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