4 methods override ServiceModifierInterface::alter()

CoreServiceProvider::alter in core/lib/Drupal/Core/CoreServiceProvider.php
Alters the UUID service to use the most efficient method available.
InstallerServiceProvider::alter in core/lib/Drupal/Core/Installer/InstallerServiceProvider.php
Modifies existing service definitions.
ServiceProviderBase::alter in core/lib/Drupal/Core/DependencyInjection/ServiceProviderBase.php
Modifies existing service definitions.
UpdateServiceProvider::alter in core/lib/Drupal/Core/Update/UpdateServiceProvider.php
Modifies existing service definitions.

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