solidity/docs/060-breaking-changes.rst

********************************
Solidity v0.6.0 Breaking Changes
********************************

This section highlights the main breaking changes introduced in Solidity
version 0.6.0, along with the reasoning behind the changes and how to update
affected code.
For the full list check
`the release changelog <https://github.com/ethereum/solidity/releases/tag/v0.6.0>`_.


Syntactic Only Changes
======================

This section lists purely syntactic changes that do not affect the behavior of existing code.

* Conversions from external function types to ``address`` are now disallowed. Instead external
  function types have a member called ``address``, similar to the existing ``selector`` member.
* Conversions from ``address`` to ``address payable`` are now possible via ``payable(x)``, where
  ``x`` must be of type ``address``.

* Function ``push(value)`` for dynamic storage arrays do not return the new length anymore.

* The new keyword ``abstract`` can be used to mark contracts as abstract. It has to be used
  if a contract does not implement all its functions.

* Libraries have to implement all their functions, not only the internal ones.

* New reserved keywords: ``virtual``.

Semantic Only Changes
=====================

This section lists the changes that are semantic-only, thus potentially
hiding new and different behavior in existing code.


Semantic and Syntactic Changes
==============================

This section highlights changes that affect syntax and semantics.

* The resulting type of an exponentiation is the type of the base. It used to be the smallest type
  that can hold both the type of the base and the type of the exponent, as with symmentric
  operations. Additionally, signed types are allowed for the base of the exponetation.

* The unnamed function commonly referred to as "fallback function" was split up into a new
  fallback function that is defined using the ``fallback`` keyword and a receive ether function
  defined using the ``receive`` keyword. If present, the receive ether function is called
  whenever the call data is empty. The new fallback function is called when no
  other function matches.  It can be payable in which case it may accept value
  or non-payable in which case transactions not matching any other function
  which send value will revert. If you only implement the receive and not the fallback function, calling a non-existing function on your contract in error is not possible anymore. Unless you are following an upgrade or proxy
  pattern, you should not need to implement the fallback function.


How to update your code
=======================

This section gives detailed instructions on how to update prior code for every breaking change.

* Change ``address(f)`` to ``f.address`` for ``f`` being of external function type.

* Replace ``function () external [payable] { ... }`` by either ``receive() external payable { ... }``, ``fallback() external [payable] { ... }`` or both. Prefer using a ``receive`` function only, whenever possible.

* Change ``uint length = array.push(value)`` to ``array.push(value);``. The new length can be
  accessed via ``array.length``.

New Features
============

 * The :ref:`try/catch statement <try-catch>` allows you to react on failed external calls.
 * Yul and Inline Assembly have a new statement called ``leave`` that exits the current function.


Deprecated Elements
===================

This section lists changes that deprecate prior features or syntax.


.. _interoperability_060:

Interoperability With Older Contracts
=====================================