syntax: Does anyone know how to send a payable function with a fixed amount?

[mattjaf]

I would of imagined it would have been something like

function donate() public payable(amount) {
//logic
}

The compiler doesn't seem to agree...

I'm sure theirs a way to do it,

---

Err, I must of been really tired when I wrote that.

i mean like having

    function Atk() public payable { 
        
        ReentranceInstance.donate{value: msg.value }(address(this));

        ReentranceInstance.withdraw{gas: 4000000}(test);
    }

So its a one click wonder with a payable transation without having to manually enter a value

When i change {value: msg.value} to {value: test} it fails cuz it trys to send it from the contract and the contract doesn't have a balance

It works when I get the value for test and manually send the transactions with eth

When I try to call the function within another function such as Atk{value: test}(); it doesn't compile saying that it has to be an external operation

If that makes sense.

---

Use Cases:

Proxy transactions.

Some other concepts would be like instead of using a require/if statement, a payable transaction could possibly only be sent with a certain amount of eth

---

I was thinking about creating an EIP, if its not possible

[pappyJ]

You are missing something bro

function donate() public payable(uint256 amount) {
//logic
}

then inside your logic you can make the validation to make sure the amount you desired is passed before function executes . example below

function donate() public payable(uint256 amount) {
require(msg.value == 1 ether, 'Amount must be equal to 1 ether')
//remaining logic
}

[mattjaf]

When I try adding parameters to the payable modifier, as such , the compiler throws

from solidity:
ParserError: Expected '{' but got '('
  --> ethernaut/ReentryAttack.sol:20:37:
   |
20 |     function Attack() public payable(uint256 test) {

I updated the question

[Muhammad-Abdullah012]

function donate() public payable {
   // logic
}

And you can access amount using special variable (only accessible in payable functions).
The variable is: msg.value and the amount it returns is in wei ...

[PatrickAlphaC]

Something like this would require 1 ETH

   function donate() public payable {
        require(msg.value == 1 ether, 'Amount must be equal to 1 ether');
            //remaining logic
    }

[mattjaf]

It throws a gas estimation error, cuz it doesn't automatically calculate the msg.value and prompt the tx.orgin the amount needed to be sent.

    function Attack() public payable {
        require(msg.value == test, 'Amount must be equal to test ether');
        ReentranceInstance.donate{value: test }(address(this));
        ReentranceInstance.withdraw{gas: 4000000}(test);
    }
    ``` 

[PatrickAlphaC]

cuz it doesn't automatically calculate the msg.value and prompt the tx.orgin the amount needed to be sent

You want the blockchain to prompt you for how much to spend? That's something you'd build into a front end. I guess I'm not sure what you're asking.