Questions tagged [interfaces]

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How bad is it to change a function inside ERC721 interface?

I'm creating a NFT and I want the transferFrom function to be payable. In order to do so I need to edit the ERC721 interface and make that function payable also there. If I do so everything compiles ...
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1answer
24 views

What does mutability guarantees mean in erc721

Some functions from ERC-721 interface contain payable modifiers. function transferFrom(address _from, address _to, uint256 _tokenId) external payable; I was wondering why it is payable and found ...
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Nested usage of interfaces?

Using solidity ^4.x, it seems I can use an interface as a parameter type in a function from a different interface. Example: interface IERC20 { function transfer() external; } import "./IERC20....
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File import callback not supported import “./IERC20.sol”;

when I try to compile my contract I see errors like this : DemirelToken.sol https://eksiup.com/p/4z49413damc3 here's the code : pragma solidity ^0.5.0; import "node_modules/openzeppelin-...
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Why would I use interfaces in this case?

I see suggestions here and there to import an interface instead of the whole contract to reduce contract's bytecode and deployment costs. Consider the following structures: contract Storage { ...
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1answer
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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 ...
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1answer
260 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 ...
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1answer
42 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: ...
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1answer
73 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)...
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3answers
96 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 ...
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2answers
60 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 ...
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1answer
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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?
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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: ...
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1answer
65 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 ...
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1answer
77 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 ...
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1answer
65 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 ...
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1answer
63 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 ...
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1answer
61 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 ...
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1answer
308 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 ...
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2answers
117 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 ...
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1answer
38 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 "...
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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 ...
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1answer
73 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....
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2answers
24 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?
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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 ...
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1answer
52 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 ...
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2answers
250 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:...
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1answer
93 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 ...
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2answers
348 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 (...
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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....
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1answer
161 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 ...
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1answer
274 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 ...
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2answers
129 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 ...
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1answer
443 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 ...
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1answer
206 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.
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1answer
320 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 ...
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1answer
75 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 ...
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2answers
406 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 ...
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3answers
177 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 ...
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2answers
429 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,...
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0answers
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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 ...
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1answer
397 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[...
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1answer
98 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, ...
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1answer
409 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` ...
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2answers
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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) ...
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1answer
456 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 = ...
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1answer
792 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[...
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1answer
86 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.
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1answer
652 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 ...
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1answer
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(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 ...