A intro to Casper smartcontract dev.

Just a counter, start from 0.

Install the Rust and the WebAssembly Binary Toolkit.

make prepare

When on the first version dev. We use add_contract_version on the call to upgrade the smart contract. And the counter value put on global state is before upgrade. After update, The global state is been interrupted. So after update, we use storage::write or storage::add will have unreachable problem. And use context to query the counter, It will shows the value before upgrade.

Solve this problem. When we create the counter before update, we create a URef to this gloabal state and pass it on the add_contract_version's parameter named_keys. Then on the contract upgrade

P.S. You can consider URef as pointer. You can consider the call function as a class's once init. We use this function to create other member function.(If you want upgrade contract twice, you can make a funtion like upgrade)