6 methods override MigrateSourceInterface::__toString() in Drupal 8

ContentEntity::__toString in core/modules/migrate_drupal/src/Plugin/migrate/source/ContentEntity.php

Allows class to decide how it will react when it is treated like a string.

EmbeddedDataSource::__toString in core/modules/migrate/src/Plugin/migrate/source/EmbeddedDataSource.php

Allows class to decide how it will react when it is treated like a string.

EmptySource::__toString in core/modules/migrate/src/Plugin/migrate/source/EmptySource.php

Allows class to decide how it will react when it is treated like a string.

MigrateExternalTranslatedTestSource::__toString in core/modules/migrate/tests/modules/migrate_external_translated_test/src/Plugin/migrate/source/MigrateExternalTranslatedTestSource.php

Allows class to decide how it will react when it is treated like a string.

SqlBase::__toString in core/modules/migrate/src/Plugin/migrate/source/SqlBase.php

Prints the query string when the object is used as a string.

StubSourcePlugin::__toString in core/modules/migrate/tests/src/Unit/MigrateSourceTest.php

Allows class to decide how it will react when it is treated like a string.