src/ContainerBuilder.php
public function setContainerName(string $containerName) 
    {
        if (empty($containerName) || !(preg_match('/^[a-zA-Z0-9\\\\_]*$/', $containerName)) || is_numeric($containerName[0]))
        {
            throw new ContainerBuilderException('The container name cannot be empty, start with a number or contain sepcial characters except "\\".');
        }

        if ($containerName[0] === "\\")
        {
            $containerName = substr($containerName, 1);
        }

        $this->containerClassName = $this->containerName = $containerName;

        // check if we need to generate a namespace
        if (($pos = strrpos($containerName, "\\")) !== false)
        {
            $this->containerNamespace = substr($containerName, 0, $pos);
            $this->containerClassName = substr($containerName, $pos + 1);
        }
    }
public function setContainerName(string $containerName) 
    {
        if (empty($containerName) || !(preg_match('/^[a-zA-Z0-9\\\\_]*$/', $containerName)) || is_numeric($containerName[0]))
        {
            throw new ContainerBuilderException('The container name cannot be empty, start with a number or contain sepcial characters except "\\".');
        }

        if ($containerName[0] === "\\")
        {
            $containerName = substr($containerName, 1);
        }

        $this->containerClassName = $this->containerName = $containerName;

        // check if we need to generate a namespace
        if (($pos = strrpos($containerName, "\\")) !== false)
        {
            $this->containerNamespace = substr($containerName, 0, $pos);
            $this->containerClassName = substr($containerName, $pos + 1);
        }
    }
Sets the container name
This will also update the "containerClassName" and "containerNamespace"

@param string            $containerName
@return void