EternalStorage¶
Description¶
This is an implementation of the well-known eternal storage smart contract pattern, described in more detail here and here.
In short, it is a key-value store for variables which are retrieved by a byte string, typically a hash of their name and an index.
The contract is architected this way so that the access pattern is uniform and the memory layout is not dependent on implementation or compilation details. In this way, smart contracts can retain state between updates while minimising the difficulty and expense of migrating this information.
Each type of variable has its own mapping, along with getters and setters. As this entails some replication, this document will express functions and variables generically with the type variable š¯•‹, where š¯•‹ \in {uint, string, address, bytes, bytes32, bool, int}. This notation is used slightly abusively, standing in for both names and types; in the former case, substitution is in camelCase. More complex types, such as structs and nested mappings, are not supported.
Source: EternalStorage.sol
Architecture¶
Inheritance Graph¶
Variables¶
š¯•‹Storage¶
A mapping from keys to values of type š¯•‹.
Type: mapping(bytes32 => š¯•‹)
Functions¶
constructor¶
Initialises the inherited State instance.
Details
Signature
constructor(address _owner, address _associatedContract) public
Superconstructors
getš¯•‹Value¶
Return the value associated with a particular key in the š¯•‹Storage mapping.
In theory this function could be eliminated by making the storage mapping public, but providing it makes accessor naming more consistent.
Details
Signature
getš¯•‹Value(bytes32 record) external view returns (š¯•‹)
Note
If š¯•‹ is string or bytes, the result is returned in memory rather than storage.
setš¯•‹Value¶
Sets the value associated with a particular key in the š¯•‹Storage mapping.
Details
Signature
setš¯•‹Value(bytes32 record, š¯•‹ value) external
Modifiers
deleteš¯•‹Value¶
Deletes the value associated with a particular key in the š¯•‹Storage mapping.