> ## 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 Throw Expression The `throw` keyword in Dart is an expression used to raise an exception or error at runtime. Because Dart treats `throw` as an expression rather than a statement, it evaluates to the bottom type `Never`. This allows it to be embedded directly within other expressions, as the compiler understands that the expression will never successfully return a value to its surrounding context. ## Syntax The basic syntax consists of the `throw` keyword followed by an expression that evaluates to a non-null Dart object: ```dart theme={"dark"} throw ; ``` ## Technical Characteristics **1. The `Never` Type** When a `throw` expression is evaluated, the current control flow is immediately interrupted. The Dart analyzer assigns the return type of a `throw` expression as `Never`. Because `Never` is a subtype of all other types in Dart's sound type system, a `throw` expression satisfies the type checker in any context requiring a specific return type. **2. Arbitrary Object Throwing** Unlike languages that restrict exceptions to specific base classes (e.g., `Throwable` or `Exception`), Dart permits the throwing of *any* non-null object. While typically used with instances of `Exception` or `Error`, throwing primitives or custom objects is syntactically valid. ```dart theme={"dark"} throw FormatException('Invalid format'); // Standard exception object throw 'String error'; // Valid, throws a String object throw 404; // Valid, throws an int object ``` ## Expression Contexts Because `throw` is an expression, it can be utilized in concise syntactic constructs where standard statements are invalid. **Arrow Functions** It can serve as the single expression body of an arrow function. ```dart theme={"dark"} void triggerError() => throw StateError('Invalid state'); ``` **Ternary Operators** It can be used as one or both branches of a conditional expression. ```dart theme={"dark"} int parseValue(bool isValid) { return isValid ? 100 : throw ArgumentError('Invalid flag'); } ``` **Null-Aware Operators** It can be placed on the right-hand side of the null-coalescing operator (`??`) to enforce non-nullability during assignment. ```dart theme={"dark"} String processName(String? inputName) { String name = inputName ?? throw ArgumentError.notNull('inputName'); return name; } ```

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