generator.void

Code example

<?php declare(strict_types = 1);

/**
 * @return \Generator<int, int, void, void>
 */
function numbers(): \Generator
{
	yield 1;
	$value = yield 2;
}

Why is it reported?

The generator declares void as its send type (the TSend template parameter of Generator), meaning that no value is sent back into the generator via Generator::send(). Using the result of a yield expression when the send type is void will always produce null, which indicates a logic error -- the code appears to expect a value to be sent into the generator, but the type declaration says otherwise.

How to fix it

If the generator needs to receive values via send(), declare the correct send type:

 /**
- * @return \Generator<int, int, void, void>
+ * @return \Generator<int, int, string, void>
  */
 function numbers(): \Generator
 {
 	yield 1;
 	$value = yield 2;
 }

If the generator does not need to receive values, remove the unused assignment:

 /**
  * @return \Generator<int, int, void, void>
  */
 function numbers(): \Generator
 {
 	yield 1;
-	$value = yield 2;
+	yield 2;
 }