> ## 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 Show Combinator
The `show` combinator is a directive modifier in Dart used alongside `import` or `export` statements to act as an explicit inclusion whitelist. It restricts the visibility of an external library's API by selectively bringing only the specified top-level declarations (classes, functions, variables, or typedefs) into the current library's namespace, leaving all unlisted declarations inaccessible.
```dart theme={"dark"}
import 'package:library_name/library_name.dart' show DeclarationOne, declarationTwo;
export 'package:library_name/library_name.dart' show DeclarationOne;
```
## Mechanics and Syntax Rules
* **Comma-Separated Identifiers:** Multiple declarations must be separated by commas. The identifiers must exactly match the exported names from the target library.
* **Namespace Isolation:** Declarations omitted from the `show` list are not bound in the importing library's scope. Attempting to reference an unlisted declaration results in a static analysis error (`undefined_identifier`).
* **Chaining with Prefixes:** The `show` combinator can be chained with the `as` directive. The filtering occurs before the prefix is applied to the namespace.
* **Export Re-routing:** When used with `export`, the `show` combinator restricts which parts of an external library are re-exported as part of the current library's public API.
## Code Illustration
Given an external library `arithmetic.dart`:
```dart theme={"dark"}
// arithmetic.dart
int add(int a, int b) => a + b;
int subtract(int a, int b) => a - b;
int multiply(int a, int b) => a * b;
```
Applying the `show` combinator in the importing library:
```dart theme={"dark"}
// main.dart
import 'arithmetic.dart' show add, subtract;
void main() {
print(add(5, 3)); // Valid: explicitly shown
print(subtract(5, 3)); // Valid: explicitly shown
// print(multiply(5, 3));
// Error: The function 'multiply' isn't defined.
}
```
## Combinator Chaining
When combining `show` with a namespace prefix (`as`), the syntax requires the prefix declaration to precede the combinator:
```dart theme={"dark"}
import 'arithmetic.dart' as math show add;
void main() {
print(math.add(5, 3)); // Valid
}
```
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