<?php
namespace VendorNameModuleNameSetup;
use MagentoEavSetupEavSetup;
use MagentoEavSetupEavSetupFactory;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{

private $eavSetupFactory;

/**
* Init
*
* @param EavSetupFactory $eavSetupFactory
*/
public function __construct(EavSetupFactory $eavSetupFactory)
{
    $this->eavSetupFactory = $eavSetupFactory;
}

public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
{
            /** @var EavSetup $eavSetup */
            $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
            /**
            * Add attributes to the eav/attribute
            */

            $eavSetup->addAttribute(
                MagentoCatalogModelProduct::ENTITY,
                'custom_attribute',
                [
                    'group' => 'General',
                    'type' => 'int',
                    'backend' => '',
                    'frontend' => '',
                    'label' => 'Custom Label',
                    'input' => 'boolean',
                    'class' => '',
                    'source' => MagentoEavModelEntityAttributeSourceBoolean::class,
                    'global' => MagentoEavModelEntityAttributeScopedAttributeInterface::SCOPE_GLOBAL,
                    'visible' => true,
                    'required' => false,
                    'user_defined' => false,
                    'default' => '1',
                    'searchable' => false,
                    'filterable' => false,
                    'comparable' => false,
                    'visible_on_front' => false,
                    'used_in_product_listing' => false,
                    'unique' => false,
                    'apply_to' => 'simple,configurable,virtual,bundle,downloadable'
                ]
            );
    }
}