The compiled bytecode of a contract has two sections

1. Contract initialization

Initialization bytecode is executed only once during the deployment of the contract and is not stored in the storage

600a600c600039600a6000f3602a60505260206050f3

• The leading 600a600c600039600a6000f3 part is initialization bytecode

1. Runtime bytecode

This comprises anything (methods, events, constants, etc.) in the contract except constructor code

0x6057361d000000000000000000000000000000000000000000000000000000000000000a

• The contract extracts the first 4 bytes of this calldata, which is the function selector, and basically runs a series of if / else statements to decide which function matches it

object "Box" {
    code {
        // initialization code
    }

    object "runtime" {
        code {
            // runtime code within sub-object
        }
    }
}

retrieve() however, instead of returning the value upfront, stores it in memory (mstore(memloc, val))