How to get the address of a contract deployed by another contract?

Question

// deploy a new purchase contract
function newPurchase()
    public
    payable
    returns(address newContract)
{
    Purchase c = (new Purchase).value(msg.value)(address(msg.sender));
    contracts.push(c);
    lastContractAddress = address(c);
    return c;
}

I was going through this code: https://github.com/jacksonng77/StartEscrow/blob/master/StartEscrow.sol

and I got to this part of the code (see code above) where I am having difficulty trying to understand it. (The full code is on the link above) The difficulty is particularlly on this line

Purchase c = (new Purchase).value(msg.value)(address(msg.sender));

How does this return the address of the contract? Why are we doing a

.value(msg.value)

and what is the work of

(address(msg.sender));

Also this line...

lastContractAddress = address(c)

why can I just say

lastContractAddress = c;

what is the purpose of address()?

Answer 1

Your function is not a view function because it modifies and thus will be a transaction so it will not return a value , simply the tx receipt.

The value can be returned to another function however, just not to the user. You'll have to use log for that.

• (new Purchase) - creates new contract , returns an instance so we need to typecast to address (this is since 0.4.15 ish)
• .value(msg.value) - send some ether to the new contract we're creating
• address(msg.sender) - should be just msg.sender and is a parameter for the constructor of the new contract

When not sending value upon creation to the new contract we could just say

new Purchase(msg.sender)