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Documenting bytes to fixed bytes conversion.

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Co-authored-by: chriseth <chris@ethereum.org>

Co-authored-by: Alex Beregszaszi <alex@rtfs.hu>
This commit is contained in:
Djordje Mijovic 2021-04-13 09:07:23 +02:00
parent eb457064b1
commit 337adee395
3 changed files with 26 additions and 8 deletions
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1
Changelog.md
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@ -1,6 +1,7 @@
### 0.8.5 (unreleased)
Language Features:
* Allowing conversion from ``bytes`` and ``bytes`` slices to ``bytes1``/.../``bytes32``.
Compiler Features:

21
docs/types/conversion.rst
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@ -99,6 +99,27 @@ rules explicit::
uint8 d = uint8(uint16(a)); // d will be 0x34
uint8 e = uint8(bytes1(a)); // e will be 0x12
``bytes`` arrays and ``bytes`` calldata slices can be converted explicitly to fixed bytes types (``bytes1``/.../``bytes32``).
In case the array is longer than the target fixed bytes type, truncation at the end will happen.
If the array is shorter than the target type, it will be padded with zeros at the end.
::
// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.5;
contract C {
bytes s = "abcdefgh";
function f(bytes calldata c, bytes memory m) public view returns (bytes16, bytes3) {
require(c.length == 16, "");
bytes16 b = bytes16(m); // if length of m is greater than 16, truncation will happen
b = bytes16(s); // padded on the right, so result is "abcdefgh\0\0\0\0\0\0\0\0"
bytes3 b1 = bytes3(s); // truncated, b1 equals to "abc"
b = bytes16(c[:8]); // also padded with zeros
return (b, b1);
}
}
.. _types-conversion-literals:
Conversions between Literals and Elementary Types

12
docs/types/reference-types.rst
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@ -492,7 +492,7 @@ Array slices are useful to ABI-decode secondary data passed in function paramete
::
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
pragma solidity >0.8.4 <0.9.0;
contract Proxy {
/// @dev Address of the client contract managed by proxy i.e., this contract
address client;
@ -504,13 +504,9 @@ Array slices are useful to ABI-decode secondary data passed in function paramete
/// Forward call to "setOwner(address)" that is implemented by client
/// after doing basic validation on the address argument.
function forward(bytes calldata _payload) external {
// Since ABI decoding requires padded data, we cannot
// use abi.decode(_payload[:4], (bytes4)).
bytes4 sig =
_payload[0] |
(bytes4(_payload[1]) >> 8) |
(bytes4(_payload[2]) >> 16) |
(bytes4(_payload[3]) >> 24);
bytes4 sig = bytes4(_payload[:4]);
// Due to truncating behaviour, bytes4(_payload) performs identically.
// bytes4 sig = bytes4(_payload);
if (sig == bytes4(keccak256("setOwner(address)"))) {
address owner = abi.decode(_payload[4:], (address));
require(owner != address(0), "Address of owner cannot be zero.");