code: public function inject(string ...$methods): Binding
      {
          if ($this->definition->injects === null) {
              $this->definition->injects = \array_fill_keys($methods, true);
          } else {
              foreach ($methods as $f) {
                  $this->definition->injects[$f] = true;
              }
          }
          
          return $this;
      }
docs: Define methods to be used for mutator injection.
  
  Mutator injection is a variation of setter injection that requires the injection method to return a new
  instance of the object that is the receiver of the injection and return it. Injector methods should have
  a signature like "public withFoo(Foo $foo): self" and must not return the same object (this is enforced
  to avoid mutable object state).