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[CORDA-3082] Update app upgrade notes to document source incompatibility (#5344)

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James Higgs 2019-08-16 10:53:31 +01:00 committed by Shams Asari
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docs/source/app-upgrade-notes.rst
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@ -4,8 +4,8 @@
<script type="text/javascript" src="_static/jquery.js"></script>
<script type="text/javascript" src="_static/codesets.js"></script>
Upgrading apps to Corda 4
=========================
Upgrading CorDapps to newer Platform Versions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These notes provide instructions for upgrading your CorDapps from previous versions. Corda provides backwards compatibility for public,
non-experimental APIs that have been committed to. A list can be found in the :doc:`corda-api` page.
@ -23,6 +23,73 @@ from the new features in the latest release.
.. contents::
:depth: 3
Upgrading apps to Platform Version 5
====================================
This section provides instructions for upgrading your CorDapps from previous versions to take advantage of features and enhancements introduced
in platform version 5.
.. note:: If you are upgrading from a platform version older than 4, then the upgrade notes for upgrading to Corda 4 (below) also apply.
Step 1. Handle any source compatibility breaks (if using Kotlin)
----------------------------------------------------------------
The following code, which compiled in Platform Version 4, will not compile in Platform Version 5:
.. container:: codeset
.. sourcecode:: kotlin
data class Obligation(val amount: Amount<Currency>, val lender: AbstractParty, val borrower: AbstractParty)
val (lenderId, borrowerId) = if (anonymous) {
val anonymousIdentitiesResult = subFlow(SwapIdentitiesFlow(lenderSession))
Pair(anonymousIdentitiesResult[lenderSession.counterparty]!!, anonymousIdentitiesResult[ourIdentity]!!)
} else {
Pair(lender, ourIdentity)
}
val obligation = Obligation(100.dollars, lenderId, borrowerId)
Compiling this code against Platform Version 5 will result in the following error:
``Type mismatch: inferred type is Any but AbstractParty was expected``
The issue here is that a new ``Destination`` interface introduced in Platform Version 5 can cause type inference failures when a variable is
used as an ``AbstractParty`` but has an actual value that is one of ``Party`` or ``AnonymousParty``. These subclasses
implement ``Destination``, while the superclass does not. Kotlin must pick a type for the variable, and so chooses the most specific
ancestor of both ``AbstractParty`` and ``Destination``. This is ``Any``, which is not a valid type for use as an ``AbstractParty`` later.
(For more information on ``Destination``, see the :doc:`changelog` for Platform Version 5, or the KDocs for the interface
`here <https://docs.corda.net/head/api/kotlin/corda/net.corda.core.flows/-destination.html>`__)
Note that this is a Kotlin-specific issue. Java can instead choose ``? extends AbstractParty & Destination`` here, which can later be used
as ``AbstractParty``.
To fix this, an explicit type hint must be provided to the compiler:
.. container:: codeset
.. sourcecode:: kotlin
data class Obligation(val amount: Amount<Currency>, val lender: AbstractParty, val borrower: AbstractParty)
val (lenderId, borrowerId) = if (anonymous) {
val anonymousIdentitiesResult = subFlow(SwapIdentitiesFlow(lenderSession))
Pair(anonymousIdentitiesResult[lenderSession.counterparty]!!, anonymousIdentitiesResult[ourIdentity]!!)
} else {
// This Pair now provides a type hint to the compiler
Pair<AbstractParty, AbstractParty>(lender, ourIdentity)
}
val obligation = Obligation(100.dollars, lenderId, borrowerId)
This stops type inference from occurring and forces the variable to be of type ``AbstractParty``.
Upgrading apps to Platform Version 4
====================================
This section provides instructions for upgrading your CorDapps from previous versions to platform version 4.
Step 1. Switch any RPC clients to use the new RPC library
---------------------------------------------------------