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Is it possible for contract X to read the storage of contract Y without making a transaction?
I think I understand how I can make X call a function on Y using a callback pattern. But since I only want to read the storage of Y - and they are on the same ledger - the data should be readily available to X without making any transactions?
For an updated answer, views have been added when the Hangzhou protocol was activated.
They are known as "On-chain views" and their usage with the various high level contract languages can be found searching this term.
It is not possible for a contract X to access the storage of contract Y against Y's will. The main reason to forbid this is to prevent ticket steal. For contract Y, allowing contract X to read some part of the storage is typically done using the view pattern of TZIP 4 but in the future first-class views might be added to Michelson.
