Questions tagged [interfaces]
The interfaces tag has no usage guidance.
1
vote
1answer
31 views
ERC721: Interface ID Registration
Why we need to register Interface ID in ERC721 token. I was just going through the openzeppelin-solidity erc721 code and curious to know that why we need to use this. That interface id register code ...
2
votes
1answer
73 views
How to interact with ERC20 interface?
My target is to send from the ERC20Wrapper.sol deployed contract BAT tokens to my hard coded address.
I've created ERC20 Interface:
pragma solidity 0.4.18;
interface ERC20 {
function ...
0
votes
1answer
40 views
DAPP WALLET transaction always fails
To improve my skills in solidity I'm working on a "wallet dapp". Based on smart contracts only, users can send ERC20 to another wallet. It works like that:
user gives the following parameters: ...
0
votes
1answer
26 views
Solidity, how to cast SmartContract type to address
I am currently a bit stuck with my contract, the issue is following:
I define a smartcontract type which is used for another address (aka address is smartcontract that provides the specified interface)...
0
votes
3answers
49 views
REMIX:This contract does not implement all functions and thus cannot be created
What should I do?
pragma solidity ^0.4.21;
contract ScoreInterface {
function hit() public;
function score() public view returns (uint);
}
This contract does not implement all ...
0
votes
2answers
32 views
Solidity how to check if user is already used another contract?
I am trying to figure out how to set up a simple communication between contracts.
For example, we have a contract Passport, in which the user writes his data. After that, through the Election ...
1
vote
1answer
15 views
In case we have an interface written in a seperate .sol file how do we migrate it successfully?
HI consider i have 3 smart contracts A,B,C.
I have a separate file D.sol which is an interface used in all A,B and C.
What would the migration script look like for this project?
1
vote
0answers
19 views
Can I extend the interface of a contract without redeploying it?
The case I'm dealing with is a contract which should serve as a Data Abstraction Layer.
So ideally, it should provide only getter functions and setter functions.
For example, my interface is:
...
0
votes
1answer
42 views
how to parse values returned by one contract into another?
I've two contracts deployed one is UserRegistration and another is Exam
I've getUser(uint id) method to fetch data of particular user using users mapping,
function getUser(uint _id) public constant ...
1
vote
1answer
42 views
Can abstract contracts in solidity have state variables?
I want to have one deployed contract with my data structure and all data and another separate contract with functions that calls the deployed contract. If i've understood things correctly, one should ...
0
votes
1answer
38 views
Enum in interfaces
Following the documentation I try to add a enum to my interface. Inside the interface I have a method called get that returns one of the enum value. Im trying to add the enum to the interface, because ...
0
votes
1answer
48 views
Interfaces implementation visibility
I have this interface:
pragma solidity ^0.4.24;
interface EventsInterface
{
function removeValueFromArray(uint _userId, uint[] array) external
returns(uint[]);
}
And this contract:
pragma ...
0
votes
1answer
42 views
Interface overriding
I have two contracts. One of them inherits another. Inside the parent contract I have the interface
interface Token {
function transfer(address to, uint256 value) external returns (bool);
}
I ...
0
votes
1answer
144 views
Interfaces in solidity
I have one interface like the following:
pragma solidity ^0.4.11;
interface TokenInterface {
function transfer(address recipient, uint amount) external returns(bool);
}
And the implementation in ...
1
vote
2answers
102 views
Variables in interfaces
Im trying to implement my first interface. But when I try to add a new variable, Remix tell me that can´t add variables in interfaces.
It have sense to set the fixed variables that the extended ...
1
vote
1answer
33 views
Simple but important question: How to get the value of contract's state when using Metamask? [closed]
I'm designing an HTML file (or a user interface: UI) for my smart contract.
let's assume that my contract has a state as follows:
address public owner;// it is set to "...
0
votes
0answers
57 views
Why is not Metamask invoked in my user interface?
I'm running a private Ethereum blockchain on my computer.
I've installed Metamask on my chrome as well.
I can create an account on metamask, and then interact with my smart contract deployed on my ...
0
votes
1answer
56 views
Error in external function parameter defination for an interface
Dear community members,
I have come across an error while defining an interface (just using the standard one interface ERC721TokenReceiver)
this interface is mentioned in this link https://github....
1
vote
2answers
20 views
Is it possible to have an optional property or method in an interface?
I currently can't deploy any contract which doesn't adhere 100% to the specified interface(s). Is there a way to mark some properties or methods as optional and, if not, is this a planned feature?
1
vote
2answers
73 views
Why are all parameters prepended by an underscore in ERC interfaces? [duplicate]
For instance, both ERC-721 and ERC-725 have underscores(_) before any function parameter.
I understand that normally their goal is to avoid variable overloading. However, what is the rationale for ...
0
votes
1answer
44 views
Contract Using An Interface Is Not Compiling
I am learning Solidity and I am using Remix to experiment and enhance my learning. I am currently trying to create a simple contract that uses an Interface.
pragma solidity ^0.4.19;
contract ...
0
votes
1answer
63 views
How can you approve a token through an interface?
I have an interface to Dai from my contract and want to allow a user to approve the contract to transfer their Dai. Dai uses DSToken code which has an approve function that relies on msg.sender:
...
2
votes
2answers
153 views
How to create Interface to read Struct in mapping?
There are 2 contracts A and B.
A has a mapping which returns Struct:
mapping (bytes32 => Cup) public cups;
How can we read the cups mapping in contract B?
Following code doesn't work for sure:...
0
votes
1answer
58 views
Should Solidity interfaces always specify return types?
I've seen interfaces in which the function definitions specify a return type, ie:
(from openZepplin's IERC721.sol)
function balanceOf(address owner) public view returns (uint256 balance);
and ...
3
votes
2answers
230 views
Can we modify ERC20 functions?
I have to create and transfer token using ERC 20.Inside the standard interface of ERC 20, we have function approve(address spender,using token) which inturn approves spender to take some token from (...
0
votes
0answers
13 views
what do I do with compiled interface output?
I created a token sale smart contract. And it has an interface that resolves to a token contract address.
Now the output folder has the compiled token sale smart json file and the interface json file....
0
votes
1answer
108 views
creating and array using type Big.Int and counting the sum of all integers inside it
Im communicating with a smart contract trying to get the balances from a list of addresses. I then want to get the sum of all balances but I am stuck on actually creating the array to store all the ...
1
vote
1answer
231 views
Smart Contract Design: Escrow/Controller contract
How would I go about creating follow: Escrow/Controller contract A which is capable of accepting ERC20tokens from contract B, and ETH from party C and do a swap when certain conditions are met.
This ...
1
vote
2answers
106 views
ERC20 Interfaces overwriting ERC721 functions - Possible to adhere to standard?
Is it possible to have a contract that both generates and manages its own NFT according to the ERC721 Standard, and is able to make calls to outside ERC20 contracts? My contract currently inherits the ...
0
votes
1answer
272 views
What are the benefits of abstract contracts?
I've seen similar questions, but none answer why people use abstract contracts. I come from a non-OOP JavaScript background, so I have some trouble understanding these things.
From the docs:
pragma ...
1
vote
1answer
161 views
Ethereum address URL
Is there a standard or a convention for URLs of Ethereum address?
That is I want clicking xxx://0x... to initiate transfer to this account.
2
votes
1answer
258 views
Why public variables aren't able to implement interface functions?
I'm curious why interfaces don't accept public variables as implementations, since public variables have getter functions generated for them.
For example why couldn't the ERC20 balanceOf interface ...
0
votes
1answer
69 views
Why standard tokens inherit interface?
I was wondering why most tokens inherit from an ERC20 interface, instead of just implementing all the functions directly. Are there are any problems that arise if the interface functions are just ...
3
votes
2answers
327 views
ERC-721 safeTransferFrom is overloaded?
According to ERC-721 interface the function safeTransferFrom seems to be overloaded:
function safeTransferFrom(address _from, address _to, uint256 _tokenId) public;
function safeTransferFrom(address ...
asked Mar 30 '18 at 8:59
Juan Ignacio Pérez Sacristán
1,1803 gold badges23 silver badges56 bronze badges
1
vote
3answers
151 views
How to detect if a contract has a particular function implemented?
I would like to detect if an address has a particular function implemented.
In this case isSafe:
interface ISafe {
function isSafe() public pure returns (bool _true);
// other functions I ...
2
votes
1answer
343 views
Anyone knows what does this contract code mean?
Refer to the link below:
https://github.com/bokkypoobah/Tokens/blob/master/contracts/MyToken.sol
Line 62:
contract ApproveAndCallFallBack {
function receiveApproval(address from, uint256 tokens,...
1
vote
0answers
45 views
Enum type in interface function declaration
I understand that you "cannot define enums" in an interface contract; but, in the contract that I am working with, some of the function declarations require an enum type as an input or output ...
0
votes
1answer
368 views
Solidity function overloading and selectors — member not unique
I have the following contract:
pragma solidity ^0.4.17;
contract test{
mapping(bytes4 => bool) internal supportedInterfaces;
uint public a;
function test() public{
supportedInterfaces[...
0
votes
1answer
86 views
Identical contract functions in interface with different inputs
In the ERC721 interface, you have two functions with the same name:
function transferFrom(address _from, address _to, uint256 _tokenId) public;
function transferFrom(address _from, address _to, ...
2
votes
1answer
339 views
How do I check in solidity if interface is supported?
In the new ERC721 documents (erc721.org), the interface says that one of the functions should be:
/**
* @dev Returns `true` if the contract implements `interfaceID` and`interfaceID` ...
2
votes
2answers
282 views
Interface initiailization
I'm following cryptozombies solidity tutorial.
In lesson 2, chapter 11 it explains how to create an interface for CryptoKitties as follows:
contract KittyInterface {
function getKitty(uint256 _id) ...
1
vote
1answer
428 views
How does the ERC20 tutorial instantiate an unimplemented interface?
I've been going through the official Ethereum token tutorial and I noticed that the provided token code includes the following lines within the approveAndCall function:
tokenRecipient spender = ...
0
votes
1answer
757 views
how to call one contract function into another contract
contract xyz {
mapping(address => bool) Users;
function add(address userAddress) {
require(userAddress != 0x0 && !Users[userAddress]);
Users[...
0
votes
1answer
73 views
Specify full ABI of another contract?
Contract A calls contract B.
Does contract A need to know B's full ABI for its external functions? Or can you just give it the interface for the functions that contract A will call.
0
votes
1answer
588 views
Very simply: setProvider is not a function
I have a very simple contract already deployed to the kovan network
I want to create a very simple web3 interface, so I'm following the truffle webpack metacoin example with the following app.js
...
4
votes
1answer
959 views
(Sub) contract vs. library vs. struct vs. Interface
First I googled and read through these questions:
Creating multiple contracts or Single contract with struct
Child contract vs struct
Why are so many examples using separated contracts (e.g. crowed ...
1
vote
1answer
417 views
Array of interfaces of contracts
In an oop language, I could do the following:
I can define an interface Foo with a function F(). I then define two classes Bar1 and Bar2 implementing this interface. I can then create an array of Foo ...
4
votes
1answer
3k views
Deploying abstract contracts and interfaces
I am trying to create a basic inheritance hierarchy with abstract/virtual formalisms. Consider the following two contracts:
Abstract Contract (IUser.sol):
contract IUser {
function addUser (...
3
votes
1answer
224 views
Best practices for interacting with other contracts
I would like to know what is the best approach and the best practices to intercat with other contracts.
Here are the MyFriendToken.sol and the MyService.sol:
MyFriendToken.sol
I would like to know ...
1
vote
0answers
51 views
What's so special about the .call() function?
All that the docs have to say about it is that it "lets the Ethereum network know we're not intending to persist any changes." So I get that it's used when not conducting a transaction.
So, I decided ...
