mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
Merge pull request #951 from Denton-L/interesting-case
Document use of smaller storage variables
This commit is contained in:
commit
52d9f89712
@ -15,6 +15,23 @@ Statically-sized variables (everything except mapping and dynamically-sized arra
|
|||||||
- If an elementary type does not fit the remaining part of a storage slot, it is moved to the next storage slot.
|
- If an elementary type does not fit the remaining part of a storage slot, it is moved to the next storage slot.
|
||||||
- Structs and array data always start a new slot and occupy whole slots (but items inside a struct or array are packed tightly according to these rules).
|
- Structs and array data always start a new slot and occupy whole slots (but items inside a struct or array are packed tightly according to these rules).
|
||||||
|
|
||||||
|
.. warning::
|
||||||
|
When using elements that are smaller than 32 bytes, your contract's gas usage may be higher.
|
||||||
|
This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller
|
||||||
|
than that, the EVM must use more operations in order to reduce the size of the element from 32
|
||||||
|
bytes to the desired size.
|
||||||
|
|
||||||
|
It is only beneficial to use reduced-size arguments if you are dealing with storage values
|
||||||
|
because the compiler will pack multiple elements into one storage slot, and thus, combine
|
||||||
|
multiple reads or writes into a single operation. When dealing with function arguments or memory
|
||||||
|
values, there is no inherent benefit because the compiler does not pack these values.
|
||||||
|
|
||||||
|
Finally, in order to allow the EVM to optimize for this, ensure that you try to order your
|
||||||
|
storage variables and ``struct`` members such that they can be packed tightly. For example,
|
||||||
|
declaring your storage variables in the order of ``uint128, uint128, uint256`` instead of
|
||||||
|
``uint128, uint256, uint128``, as the former will only take up two slots of storage whereas the
|
||||||
|
latter will take up three.
|
||||||
|
|
||||||
The elements of structs and arrays are stored after each other, just as if they were given explicitly.
|
The elements of structs and arrays are stored after each other, just as if they were given explicitly.
|
||||||
|
|
||||||
Due to their unpredictable size, mapping and dynamically-sized array types use a ``sha3``
|
Due to their unpredictable size, mapping and dynamically-sized array types use a ``sha3``
|
||||||
|
Loading…
Reference in New Issue
Block a user