Solidity - default data location for local vars

Question

Solidity documentation states that

the default (location -ronme) for local variables is storage

I understand that this makes sense so that localVar = contractStorageVar will result in localVar pointing, and not copying, contractStorageVar.

I'm trying to figure out how this works. For example, as local variables go out of scope, does their storage clear up?

Answer 1

No, storage variables are not cleared when they go out of scope. In most cases, you shouldn't be declaring local storage variables regardless, and the compiler will give you a warning if you try to.

In most cases, if you want to use types like arrays locally, you should explicitly declare them as memory variables like:

bytes memory myVariable = "abcd";

Note that the storage of your contract is essentially unlimited, but writing to storage is extremely expensive. Clearing storage (i.e. setting a nonzero byte to zero) refunds some of the gas.

If you don't intend to use a variable outside of your current scope, there's generally no reason to write the variable to storage. Note that memory variables are passed by reference as well, not copied.