Questions tagged [contract-design]
for high-level questions about the choices made during contract construction
1,664
questions
0
votes
1answer
12 views
Trying to do interaction between 2 contracts. But compilation failure showing should be declared Abstract
WinCon.sol
EnemyCon.sol
To create interaction, I am creating interface for EnemyCon in WinCon.sol, but Remix is throwing compilation error stating "EnemyCon should be marked abstract". I ...
0
votes
0answers
12 views
How to handle refer by register functionality in Dapp with Smart Contract? [duplicate]
I've just started to learn solidity programming..Firstly, I have a register page, in which the metamask opens up an popup and connect the user address to my dapp by registering the user on their ...
1
vote
1answer
39 views
How to register USER in my Smart Contract using Solidity?
I can't figure out how do we register user in smart contract and get the userdata when he/she tries to login after register through our website..I didn't see any article regarding this..Kindly ...
0
votes
1answer
15 views
An attack to my contract similar to ERC-20 approval() exploit
I have
function setNonRecurringFlow(uint256 _child, int256 _remainingSwapCredit) external;
function setRecurringFlow(
uint256 _child,
int256 _maxSwapCredit,
int256 ...
0
votes
1answer
25 views
How to implement owner check in Solidity
Is there any EIP that specifies how to implement function in contract, that let's you call any other function as contract owner, with provided signature?
I don't want to reinvent wheel.
For example:
I ...
2
votes
2answers
102 views
ETH - Pre-Paid smart contract so users don't pay transactions
I'm developing a "corporate" DApp, therefore the employees don't have any reason to "spend" their ether/gas for interacting with the contract...
Is there any way to enable each ...
0
votes
0answers
20 views
change from old to new contract address [closed]
How do I change a contract address to a token to the new one? Example: I'm trying to sent TRAT token to Mercatox and they told me you sent it from an old contract address.
2
votes
1answer
27 views
the same struct in array and mappings
Let's say I have a struct.
struct test {
uint x;
}
test[] all;
mappings(uint => test) map;
function bla(){
test memory structTest = test(5);
all.push(structTest);
map[10] = structTest;
...
1
vote
1answer
20 views
how to transfer from contract to another account or contract
I have a function:
function sendEther(address payable _to, uint amount) public payable returns (bool) {
bool success = _to.send(amount);
return success;
}
Now, how transferring ...
0
votes
0answers
9 views
solidity call function how gas gets forwarded
It's said that:
someAddress.call.value(y)() will send the provided ether and trigger
code execution. The executed code is given all available gas for
execution making this type of value transfer ...
0
votes
1answer
23 views
how do i pass by reference?
I have a couple of questions.
First:
So, In a function, i created memory array. I want to pass this memory by reference to another function..
function test2() public returns(uint a) {
uint[2] ...
1
vote
0answers
32 views
copy array from storage to memory
uint[2] testStorage;
function assemblyStorage() public returns (uint a, uint b){
testStorage[0] = 5;
testStorage[1] = 10;
uint[2] memory testMemory = testStorage;
...
0
votes
1answer
30 views
Is calling another contract via its address risky?
The below screenshot is from Andreas' book. I don't understand why this programming technique is so risky. See the text in the red block in the image.
We have the .sol file, and the Bytecode on the ...
0
votes
1answer
29 views
why does this contract ask to increase gas limit?
string test;
function assemblyStorage() public payable returns (string memory a){
test = "good";
assembly {
a:=sload(0)
}
}
I am trying to return the string ...
1
vote
0answers
17 views
why do i have to specify memory in arguments?
My function body looks like this:
function element(uint a, uint b, uint[2] memory c) public returns(uint e, uint f, uint g, uint k) {
I am wondering why do I put memory keyword before c ? I know that ...
1
vote
0answers
17 views
why mload(0) returns wrong number?
int x; // Storage slot #0
mapping (uint => uint) y; // Storage slot #1
uint [] z; // Storage slot #2
function element() public returns (uint a, uint b, uint c) {
z.push(45);...
1
vote
0answers
33 views
how do storage and memory variable work?
So, in an ordinary programming language, we have stack and heap.
Reference types such as array gets stored in heap. and the variable which holds the address(pointer) of this array is stored in stack..
...
2
votes
1answer
24 views
where does function variables get created?
function element() public returns (uint) {
uint test = 20;
return test;
}
Where would test variable be created ? in memory or stack ?
The funny thing is from testing assembly, I can see that it'...
1
vote
1answer
24 views
sload. assembly with struct - not working in solidity
struct S {
uint128 a;
uint128 b;
}
S test1;
function assemblyStorage() public returns (uint a, uint b, uint c, uint d, uint f, uint g){
test1 = S(5,10);
assembly {
a:=sload(0)
}
}
...
1
vote
1answer
21 views
how does memory layout work?
I am trying to understand how https://solidity.readthedocs.io/en/v0.7.2/internals/layout_in_memory.html works.
function test(uint a) public {
uint test1 = 20;
uint[1] testArr;
testArr[0] = ...
1
vote
1answer
22 views
How is caller's data related to bytecode?
I know that smart contract is deployed as bytecode.
When we call a function from application, we use the encoding with the help of ABI and we get some bytes. let's say 220 bytes.
These are the bytes ...
1
vote
1answer
38 views
contract inline assembly - return array parts by using assembly
I've a couple of questions.
mload function returns the data that resides on the address we pass to mload. Is this correct ?
add function is used to give us the address from 0 to whatever we pass. ...
0
votes
1answer
23 views
why separate assignments are better than single?
I've read that:
It is more gas efficient to initialize a tightly packed struct with separate assignments instead of a single assignment. Separate assignments makes it easier for the optimizer to ...
1
vote
1answer
39 views
how does contract cost less gas in structs?
I have a couple of questions.
we have int types as uint8, uint16, uint32, etc. I read that :
Normally there's no benefit to using these sub-types because Solidity
reserves 256 bits of storage ...
1
vote
1answer
38 views
Why can smart contracts receive ETH but not other ERC-20 tokens?
From what I've gathered (and I'm new to Ethereum), smart contracts can receive ETH payments and hold them through the receive/fallback blocks, but cannot directly hold ERC-20 tokens, but rather they ...
1
vote
1answer
23 views
Bundling two assets in a contract and issuing shares for them
Say you are tasked with coding a smart contract with the following features:
Users can deposit token A and receive liquidity shares in return.
The contract starts selling token A for token B ...
1
vote
2answers
53 views
Multi-signature contract with offline signing
Is it possible to create a multi-signature contract that would not require a transaction for every signature (since this is quite expensive for a higher number of transactions)?
Is it possible to ...
0
votes
1answer
25 views
Require(…) condition location in wrapped functions
If I'm wrapping functions, like below, does it make a difference whether I check the input argument in the private function or the external one? Will it save me gas cost to do it in the external one ...
0
votes
1answer
18 views
constructor input arguments or hardcoded values? best practice
What is the rationale for choosing to use constructor input arguments over hardcoded values? and what is best practice?
0
votes
1answer
27 views
Prevent Transfer of ERC20 token to contract address?
I want my ERC20 contract to be transferred to EOA addresses only and some specific contract address only.
I don't want to lose my tokens by mistakenly transferring to a contract address that cannot ...
0
votes
2answers
45 views
Revert ETH transfer to smart contract
How can I revert a transfer of ETH funds to my smart contract?
I would like to instantly revert any ETH being sent to my smart contract.
0
votes
1answer
27 views
Car Traceability
I want to deploy a smart contract for tracing cars. For example, say I am producing 10 cars
Now what I want is to create a smart contract for tracing cars.
So my smart contract will have three ...
0
votes
1answer
22 views
input argument structure for constructor in remix
how would the structure for an argument to the below constructor look like in remix?
constructor(
uint256[5] memory _a,
uint256[5] memory _b,
) public {...}
0
votes
0answers
21 views
What is the difference in the two mapping structures
Is the below mapping structure a legit way to create a restricted mapping, or is the latter best practice?
mapping(address => SomeStruct)[5] private structs;
and
mapping(address => mapping(...
2
votes
1answer
20 views
Am I locked to one solc version for upgradeable smart contracts?
I want to use delegatecall to make my contracts upgradeable.
Is it true that variable layout may break if I change the solc version and therefore I should use the same Solidity version for all future ...
0
votes
1answer
18 views
Mutual dependency of two contracts
I have the following code in AuthorTokens.sol:
Files files;
// ...
function mintAuthor(address _owner) external {
require(msg.sender == files, "System function");
...
0
votes
0answers
26 views
hardening infinite loops
What is the best way to 'harden' an infinite loop, if you are in a scenario where you would find it necessary to iterate over an array, would it be a best practice to put an assert condition in ...
0
votes
1answer
78 views
How do I count the elements of an array in solidity?
In my project, I want to count the elements of an array as follows:
struct Server{
uint sernum;
uint num;
uint data;
}
Server [] public datta;
function ...
0
votes
1answer
19 views
zero-initialisation of storage values in constructor or gas optimization
is it better to pay extra gas to initialise storage variables that are empty as zeroes in the constructor, or save the gas since the default is zero?
0
votes
1answer
31 views
Else if structure gives the wrong output
I have a little problem with a else if struture that doesn't give out the right result.
Here is the code:
pragma solidity >=0.5.16;
contract SupChain{
enum StateType {A, B, C}
...
0
votes
0answers
15 views
Unbounded loop solidity internals
Under the hood, what happens in an unbounded loop? let's say I'm trying to send tokens to an infinite amount of addresses and end up with an out of gas error. Will the function which executes the ...
0
votes
1answer
19 views
Function not returning address when using web3 provider
I have a contract that works fine when only using remix. I needed to test the block size and block number. here someone suggested me to use ganache which I did but now I don't get the output I'm ...
0
votes
0answers
16 views
Can I make a delegatecall to a Solidity contract that is compiled with a higher compiler version?
Lets say that I have the contracts A and B.
A needs to make a delegatecall to B.
A is (for some reason) compiled with a compiler version that is lower than B's compiler version.
Can I safely assume ...
0
votes
1answer
28 views
The below code gets compiled but when foo is called invalid opcode error is thrown
pragma solidity >=0.5.0 <0.7.0;
contract Mycontract{
uint256 a;
struct User
{ string name; }
User[] users;
function foo() public{
User storage user=users[0];
...
0
votes
1answer
25 views
why x(function setArr) is not being returned?
pragma solidity >=0.5.0 <0.7.0;
contract Example{
uint256[3] x;
function setArr(uint256[3] memory y) public returns(uint256[3] memory){
x=y;
return getArr(x);
}
...
0
votes
0answers
32 views
Deliver a dapp to a client, how to set as owner?
So, as a freelancer that wants to make a smart contract for a client, how do you set such client as the owner of the contract?
Would it be setting the owner variable to the eth address of the client, ...
1
vote
1answer
33 views
DApp Development- how to update dapp and keep existing data
Compare to web application that separate the application and database, we can update the application and keep the existing data.
Could you suggest me how to update dapp and keep the existing data?
1
vote
1answer
22 views
How does array.length— work?
I'm having trouble understanding why people call
array.length--
after deleting an element in an array (as seen in this answer and many others). Why is there need for doing so? When is the length of ...
1
vote
0answers
38 views
msg.sender and tx.origin - how to use them in practice? [duplicate]
I wrote a contract A that uses msg.sender for authentication: When A creates an item it stores msg.sender in itemsOwners mapping (itemOwners[itemId] = msg.sender;). Later A compares msg.sender to ...
0
votes
1answer
27 views
Issue with dynamic matrices in solidity
I have a matrix in solidity like that
string x[][]
I'm trying to write functions to return rows and colums
The following code works well:
// SPDX-License-Identifier: unlicensed
pragma solidity ^0.6.0;
...
