Solidity does not have the concept of typeof or isinstance. Given a contract address you cannot find out if this is of a particular contract. But there is a way to do it if contract has implemented the ERC165 standard.

ERC165 standard has just one method

function supportsInterface(interfaceId) public view returns (bool);

This method takes the interface id as the param and checks if the contract supports that interface. What does this mean? Solidity has in built method called type which returns the unique id of the interface. The interface you will supply here is of the contract whose type you want to check in another contract.


OpenZepplin has created a utility contract called ERC165Storage which implements the ERC165 standard and also has a method using which you can define which interfaces does the contract supports.

function _registerInterface(bytes4 interfaceId) internal;

This method can be supplied an interface id which the contract will save. If the same interface is queried for support it will return true.

OpenZepplin has created ERC165Checker to call supportsInterface on an address.

function supportsInterface(address account, bytes4 interfaceId) internal view returns (bool);

This method calls supportsInterface on the address to check if the address supports the given interfaceId.

How to use this? This is useful when you want to check if the given address is of a particular contract. But you should know before hand that the given address has implemented ERC165. Here is an example how you will use this.

The below contract inherits ERC165Storage and calls _registerInterface method in the constructor.

contract Sum is ERC165Storage, ISum {

	constructor {

	function sum(uint256 a, uint256 b) public override returns (uint256) {
		return a + b;


The below contract wants to check if the given address is of particular contract type.

contract Checker is ERC165Checker {
	function sumOrZero(address _add, uint256 a, uint256 b) public view returns (uint256) {
		uint256 answer;
		if (supportsInterface(_add, type(ISum).interfaceId)) {
			answer = ISum(_add).sum(a, b);
		return answer;


This is useful when you want to restrict what kind of contracts that can be supplied to the function. Each contract you want to allow for needs to implement ERC165 .

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