docs/070-breaking-changes.rst
Solidity v0.7.0 Breaking Changes
This section highlights the main breaking changes introduced in Solidity
version 0.7.0, along with the reasoning behind the changes and how to update
affected code.
For the full list check
the release changelog <https://github.com/argotorg/solidity/releases/tag/v0.7.0>_.
1 << x or 2 ** x)
will always use either the type uint256 (for non-negative literals) or
int256 (for negative literals) to perform the operation.
Previously, the operation was performed in the type of the shift amount / the
exponent which can be misleading.In external function and contract creation calls, Ether and gas is now specified using a new syntax:
x.f{gas: 10000, value: 2 ether}(arg1, arg2).
The old syntax -- x.f.gas(10000).value(2 ether)(arg1, arg2) -- will cause an error.
The global variable now is deprecated, block.timestamp should be used instead.
The single identifier now is too generic for a global variable and could give the impression
that it changes during transaction processing, whereas block.timestamp correctly
reflects the fact that it is just a property of the block.
NatSpec comments on variables are only allowed for public state variables and not for local or internal variables.
The token gwei is a keyword now (used to specify, e.g. 2 gwei as a number)
and cannot be used as an identifier.
String literals now can only contain printable ASCII characters and this also includes a variety of
escape sequences, such as hexadecimal (\xff) and unicode escapes (\u20ac).
Unicode string literals are supported now to accommodate valid UTF-8 sequences. They are identified
with the unicode prefix: unicode"Hello 😃".
State Mutability: The state mutability of functions can now be restricted during inheritance:
Functions with default state mutability can be overridden by pure and view functions
while view functions can be overridden by pure functions.
At the same time, public state variables are considered view and even pure
if they are constants.
Disallow . in user-defined function and variable names in inline assembly.
It is still valid if you use Solidity in Yul-only mode.
Slot and offset of storage pointer variable x are accessed via x.slot
and x.offset instead of x_slot and x_offset.
If a struct or array contains a mapping, it can only be used in storage. Previously, mapping members were silently skipped in memory, which is confusing and error-prone.
Assignments to structs or arrays in storage does not work if they contain mappings. Previously, mappings were silently skipped during the copy operation, which is misleading and error-prone.
Visibility (public / internal) is not needed for constructors anymore:
To prevent a contract from being created, it can be marked abstract.
This makes the visibility concept for constructors obsolete.
Type Checker: Disallow virtual for library functions:
Since libraries cannot be inherited from, library functions should not be virtual.
Multiple events with the same name and parameter types in the same inheritance hierarchy are disallowed.
using A for B only affects the contract it is mentioned in.
Previously, the effect was inherited. Now, you have to repeat the using
statement in all derived contracts that make use of the feature.
Shifts by signed types are disallowed. Previously, shifts by negative amounts were allowed, but reverted at runtime.
The finney and szabo denominations are removed.
They are rarely used and do not make the actual amount readily visible. Instead, explicit
values like 1e20 or the very common gwei can be used.
var cannot be used anymore.
Previously, this keyword would parse but result in a type error and
a suggestion about which type to use. Now, it results in a parser error.kind: "hexString".null are removed from JSON output.This section gives detailed instructions on how to update prior code for every breaking change.
x.f.value(...)() to x.f{value: ...}(). Similarly (new C).value(...)() to
new C{value: ...}() and x.f.gas(...).value(...)() to x.f{gas: ..., value: ...}().now to block.timestamp.x >> (256 - y) to
x >> uint(256 - y).using A for B statements in all derived contracts if needed.public keyword from every constructor.internal keyword from every constructor and add abstract to the contract (if not already present)._slot and _offset suffixes in inline assembly to .slot and .offset, respectively.