to_s:
size: 42
to_json:
first: first
product.metafields.custom["size"] =>
product.metafields.custom.size => 42

product.metafields.custom["first"] => first
product.metafields.custom.first => first

product.metafields.custom["last"] =>
product.metafields.custom.last =>

product.metafields.custom["to_h"] =>
product.metafields.custom.to_h =>

product.metafields.custom["to_liquid"] =>
product.metafields.custom.to_liquid =>