PHP Generator::throw() Method: Usage and Examples

The PHP Generator::throw API performs a focused operation on an object or value. The examples below show its effect on actual data.

Injects a Throwable into a suspended Fiber or Generator at the point where it resumes.

What Is Generator::throw in PHP?

Injects a Throwable into a suspended Fiber or Generator at the point where it resumes.

Syntax:

Generator::throw(Throwable $exception): mixed

The method accepts the following parameters:

• $exception — Required. A Throwable parameter named exception; the examples below show a supported value.

Return type declared by PHP: mixed. The value or side effect is demonstrated in the examples below.

Example 1: Basic Usage

This example uses a small input to make the main behavior visible.

<?php

$generator = (function (): Generator {
    yield "alpha" => 10;
    $response = yield "beta" => 20;
    return $response ?? "complete";
})();
try { $generator->throw(new RuntimeException("Stop")); } catch (RuntimeException $error) { echo $error->getMessage(); }

Output:

Stop

Injects a Throwable into a suspended Fiber or Generator at the point where it resumes.

Example 2: A Different Input

A different set of values shows the same operation in another situation.

<?php

$generator = (function (): Generator {
    yield "east" => 15;
    $response = yield "west" => 35;
    return $response ?? "complete";
})();
try { $generator->throw(new RuntimeException("Cancelled")); } catch (RuntimeException $error) { echo $error->getMessage(); }

Output:

Cancelled

A generator generally cannot be rewound after progressing beyond its first yield; getReturn() requires completion.

Practical Example: Applying the Feature

This example shows an application-style use of the feature, with its surrounding setup visible.

<?php

$generator = (function (): Generator {
    yield "east" => 25;
    $response = yield "west" => 55;
    return $response ?? "complete";
})();
try { $generator->throw(new RuntimeException("Interrupted")); } catch (RuntimeException $error) { echo $error->getMessage(); }

Output:

Interrupted

The code is shown for learning. Adjust the class names, inputs and error handling to suit your application.

Important Behavior and Edge Cases

• A generator generally cannot be rewound after progressing beyond its first yield; getReturn() requires completion.
• Injects a Throwable into a suspended Fiber or Generator at the point where it resumes.
• Observe differences in empty inputs, invalid states and optional extension availability where relevant.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Injects a Throwable into a suspended Fiber or Generator at the point where it resumes.
• A generator generally cannot be rewound after progressing beyond its first yield; getReturn() requires completion.
• Use the example that matches the values, runtime version and dependencies in your application.

Generator::throw is useful when its behavior matches the data structure and lifecycle of your PHP application. Choose it with a clear understanding of its preconditions and returned values.