"TypeError" for a simple program causing failure to compile, "Type address is not implicitly convertible to expected type address payable."

Question

This is my first contract (working from Lynda course). Even when I use the supplied code I still age this error for the following code with I try to compile:

TypeError: Type address is not implicitly convertible to expected type address payable. receiver = _receiver; ^-------^

Compilation failed. See above.

pragma solidity ^0.5.16;

contract ApprovalContract {

  address public sender;
  address payable public receiver;
  address constant public approver = 0xd268143B6FBD9BC6533F778052710C962eaAa68C;

  function ApprovalContracts() public {
    // tbd
  }

  function deposit(address _receiver) external payable {
    require(msg.value > 0);
    sender = msg.sender;
    receiver = _receiver;
  }

    function viewApprover() external pure returns(address) {
    return(approver);
  }

   function approve() external {
    require(msg.sender == approver);
    receiver.transfer(address(this).balance);
  }

}

Answer 1

The Error:

TypeError: Type address is not implicitly convertible to expected type address payable. receiver = _receiver; ^-------^

The compiler reports such errors whenever you assign a variable of type address to a variable of type address payable

In Solidity:

The address type comes in two flavors, which are largely identical:

• address: Holds a 20-byte value (size of an Ethereum address).
• address payable: Same as an address, but with the additional members transfer and send.

The idea behind this distinction is that address payable is an address you can send Ether to, while a plain address cannot be sent Ether

Address Data Type in Soldity

In your code:

address payable public receiver;
receiver = _receiver;

inside deposit function, here _receiver is of type address and not address payable

In order to fix this error, change deposit functions signature to:

function deposit(address payable _receiver) external payable {
    // Logic remains the same
}

Answer 2

Add payable to this line receiver.transfer(address(this).balance);

make sure you are add brackets to the receiver

Dont repeat a function name same as contract name, use constructor instead

Here the code should be according to solidity version 0.8.9

 pragma solidity ^0.8.9;

 contract ApprovalContract {

 address public sender;
 address payable public receiver;
 address constant public approver = ; //address

 constructor() {
 // tbd
 }

 function deposit(address _receiver) external payable {
 require(msg.value > 0);
 sender = msg.sender;
 receiver = _receiver;
 }

 function viewApprover() external pure returns(address) {
 return(approver);
 }

 function approve() external {
 require(msg.sender == approver);
 payable(receiver).transfer(address(this).balance);
 }
}