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41c1be2bac
`Json::Object` and related objects are not used at all, so this change removes `include/xrpl/json/Object.h` and all downstream files. There are a number of minor downstream changes as well. Full list of deleted classes and functions: * `Json::Collections` * `Json::Object` * `Json::Array` * `Json::WriterObject` * `Json::setArray` * `Json::addObject` * `Json::appendArray` * `Json::appendObject` The last helper function, `copyFrom`, seemed a bit more complex and was actually used in a few places, so it was moved to `LedgerToJson.h` instead of deleting it.
protocol
Classes and functions for handling data and values associated with the XRP Ledger protocol.
Serialized Objects
Objects transmitted over the network must be serialized into a canonical format. The prefix "ST" refers to classes that deal with the serialized format.
The term "Tx" or "tx" is an abbreviation for "Transaction", a commonly occurring object type.
Optional Fields
Our serialized fields have some "type magic" to make optional fields easier to read:
- The operation
x[sfFoo]means "return the value of 'Foo' if it exists, or the default value if it doesn't." - The operation
x[~sfFoo]means "return the value of 'Foo' if it exists, or nothing if it doesn't." This usage of the tilde/bitwise NOT operator is not standard outside of therippledcodebase.- As a consequence of this,
x[~sfFoo] = y[~sfFoo]assigns the value of Foo from y to x, including omitting Foo from x if it doesn't exist in y.
- As a consequence of this,
Typically, for things that are guaranteed to exist, you use
x[sfFoo] and avoid having to deal with a container that may
or may not hold a value. For things not guaranteed to exist,
you use x[~sfFoo] because you want such a container. It
avoids having to look something up twice, once just to see if
it exists and a second time to get/set its value.
(Real example)
The source of this "type magic" is in SField.h.