Get pool balances from BalancerV2 in Solidity

Question

I am trying to inspect the pool balances of a decentralized exchange called Balancer. The implementation is done with the main version V2.

I want to get the pool balance with

vault.getPoolTokens(0x5c6ee304399dbdb9c8ef030ab642b10820db8f56000200000000000000000014);

The contract looks like this:

contract BalancerV2 {
    IVault private constant vault = "0xBA12222222228d8Ba445958a75a0704d566BF2C8";

    function getPoolTokens() public view returns(uint) {
        return vault.getPoolTokens(0x5c6ee304399dbdb9c8ef030ab642b10820db8f56000200000000000000000014);
    }
    
}

But it gives me the following error message:

from solidity:
contracts/BalancerV2.sol:8:37: TypeError: Type literal_string "0xBA12222222228d8Ba445958a75a0704d566BF2C8" is not implicitly convertible to expected type contract IVault.
    IVault private constant vault = "0xBA12222222228d8Ba445958a75a0704d566BF2C8";
                                    ^------------------------------------------^

My question is:

How is it possible that even in the official GitHub repository they have a working example of how to initialize the vault with solidity compiler version 0.7.0 and I'm literally trying the same with getting this error?

---

By the way, the example in the documentation has a typo so it won't compile. Just in case if someone from the devs sees this.

https://dev.balancer.fi/resources/pool-interfacing#pool-balances

I am trying to compile this contract and am expecting to get this result:

tokens:  [0xba100000625a3754423978a60c9317c58a424e3D,
                0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2]
                
balances:  [5720903090084350251216632,
                7939247003721636150710]

Answer 1

Instead of:

IVault private constant vault = "0xBA12222222228d8Ba445958a75a0704d566BF2C8";

try this:

IVault private constant vault = IVault(0xBA12222222228d8Ba445958a75a0704d566BF2C8);