What is the specification of the 'this' keyword in Solidity? How does it work?
Sample code from Solidity Features · ethereum/wiki Wiki
contract Helper {
function getBalance() returns (uint bal) {
return this.balance; // balance is "inherited" from the address type
}
}
According to this guide:
Contracts Inherit all Members from Address.
It means that this is the pointer to the current instance of the type derived from Address (in your case - current instance of Helper), and balance is a member of Address.
It helps you distinguish between contract's own balance and any other balance, like in this example:
address payable x = 0xFFfFfFffFFfffFFfFFfFFFFFffFFFffffFfFFFfF;
if (address(x).balance < address(this).balance)
address(x).transfer(10);
And here is a some kind of definition (from this doc):
this: the current contract, explicitly convertible to address
this necessary? Can't someone just say if(x.balance < balance)?
Commented
Jun 15, 2017 at 4:04
this. In your example, balance will try to access a variable from the contract's storage (i.e. contract public property)
this.balance is deprecated, the correct way to get the balance of the contracts is through address(this).balance
Commented
Jun 30, 2018 at 12:50
Contract types are implicitly convertible to address and every contract inherits all members of "address" and overwrites them if necessary. If they are overwritten, the members of address can still be accessed via conversion to address:
address(myContract).send(10).
This also has the effect that all members of address can be accessed without prefix, i.e. uint x = this.balance; // access the balance parameter of the current contract.
so to summarize "This" represents the current contract instance.
balanceOf(this) is just a function to get the balance of ERC20 token for the currrent contract, however address(this).balance is the balance of Ether for a current contract.
Commented
Jun 30, 2018 at 12:48
These answers are good but they're not correct.
pragma solidity 4.24;
contract my contract {
function example() public view returns (address) {
return this;
}
}
What do you get? You get an address. The address of the contract.
It is NOT a state dependent variable or a use case of scope like in javascript, where you can use this to pull the global state into a callback.
It is NOT just an address, it can be viewed as a class variable which gives access to everything the contract has access to, think of it like a key but honestly I only use it to reference to it's own address.
For future reference, wrap it as such,
address(this)
To properly utilize.