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134 lines
5.5 KiB
ReStructuredText
134 lines
5.5 KiB
ReStructuredText
********************************
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Solidity v0.7.0 Breaking Changes
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********************************
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This section highlights the main breaking changes introduced in Solidity
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version 0.7.0, along with the reasoning behind the changes and how to update
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affected code.
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For the full list check
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`the release changelog <https://github.com/ethereum/solidity/releases/tag/v0.7.0>`_.
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Silent Changes of the Semantics
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===============================
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* Exponentiation and shifts of literals by non-literals (e.g. ``1 << x`` or ``2 ** x``)
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will always use either the type ``uint256`` (for non-negative literals) or
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``int256`` (for negative literals) to perform the operation.
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Previously, the operation was performed in the type of the shift amount / the
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exponent which can be misleading.
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Changes to the Syntax
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=====================
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* In external function and contract creation calls, Ether and gas is now specified using a new syntax:
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``x.f{gas: 10000, value: 2 ether}(arg1, arg2)``.
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The old syntax -- ``x.f.gas(10000).value(2 ether)(arg1, arg2)`` -- will cause an error.
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* The global variable ``now`` is deprecated, ``block.timestamp`` should be used instead.
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The single identifier ``now`` is too generic for a global variable and could give the impression
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that it changes during transaction processing, whereas ``block.timestamp`` correctly
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reflects the fact that it is just a property of the block.
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* NatSpec comments on variables are only allowed for public state variables and not
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for local or internal variables.
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* The token ``gwei`` is a keyword now (used to specify, e.g. ``2 gwei`` as a number)
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and cannot be used as an identifier.
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* String literals now can only contain printable ASCII characters and this also includes a variety of
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escape sequences, such as hexadecimal (``\xff``) and unicode escapes (``\u20ac``).
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* Unicode string literals are supported now to accommodate valid UTF-8 sequences. They are identified
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with the ``unicode`` prefix: ``unicode"Hello 😃"``.
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* State Mutability: The state mutability of functions can now be restricted during inheritance:
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Functions with default state mutability can be overridden by ``pure`` and ``view`` functions
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while ``view`` functions can be overridden by ``pure`` functions.
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At the same time, public state variables are considered ``view`` and even ``pure``
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if they are constants.
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Inline Assembly
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---------------
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* Disallow ``.`` in user-defined function and variable names in inline assembly.
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It is still valid if you use Solidity in Yul-only mode.
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* Slot and offset of storage pointer variable ``x`` are accessed via ``x.slot``
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and ``x.offset`` instead of ``x_slot`` and ``x_offset``.
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Removal of Unused or Unsafe Features
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====================================
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Mappings outside Storage
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------------------------
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* If a struct or array contains a mapping, it can only be used in storage.
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Previously, mapping members were silently skipped in memory, which
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is confusing and error-prone.
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* Assignments to structs or arrays in storage does not work if they contain
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mappings.
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Previously, mappings were silently skipped during the copy operation, which
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is misleading and error-prone.
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Functions and Events
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--------------------
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* Visibility (``public`` / ``external``) is not needed for constructors anymore:
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To prevent a contract from being created, it can be marked ``abstract``.
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This makes the visibility concept for constructors obsolete.
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* Type Checker: Disallow ``virtual`` for library functions:
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Since libraries cannot be inherited from, library functions should not be virtual.
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* Multiple events with the same name and parameter types in the same
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inheritance hierarchy are disallowed.
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* ``using A for B`` only affects the contract it is mentioned in.
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Previously, the effect was inherited. Now, you have to repeat the ``using``
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statement in all derived contracts that make use of the feature.
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Expressions
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-----------
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* Shifts by signed types are disallowed.
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Previously, shifts by negative amounts were allowed, but reverted at runtime.
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* The ``finney`` and ``szabo`` denominations are removed.
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They are rarely used and do not make the actual amount readily visible. Instead, explicit
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values like ``1e20`` or the very common ``gwei`` can be used.
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Declarations
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------------
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* The keyword ``var`` cannot be used anymore.
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Previously, this keyword would parse but result in a type error and
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a suggestion about which type to use. Now, it results in a parser error.
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Interface Changes
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=================
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* JSON AST: Mark hex string literals with ``kind: "hexString"``.
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* JSON AST: Members with value ``null`` are removed from JSON output.
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* NatSpec: Constructors and functions have consistent userdoc output.
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How to update your code
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=======================
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This section gives detailed instructions on how to update prior code for every breaking change.
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* Change ``x.f.value(...)()`` to ``x.f{value: ...}()``. Similarly ``(new C).value(...)()`` to
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``new C{value: ...}()`` and ``x.f.gas(...).value(...)()`` to ``x.f{gas: ..., value: ...}()``.
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* Change ``now`` to ``block.timestamp``.
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* Change types of right operand in shift operators to unsigned types. For example change ``x >> (256 - y)`` to
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``x >> uint(256 - y)``.
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* Repeat the ``using A for B`` statements in all derived contracts if needed.
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* Remove the ``public`` keyword from every constructor.
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* Remove the ``internal`` keyword from every constructor and add ``abstract`` to the contract (if not already present).
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* Change ``_slot`` and ``_offset`` suffixes in inline assembly to ``.slot`` and ``.offset``, respectively.
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