Working of Truffle

Question

The following is my code in solidity

pragma solidity ^0.4.2;

contract DappToken {
  //Constructor
  // set no of Tokens
  // Read the total number of Tokens
  uint256 public totalSupply;

  function DappToken () public {
    totalSupply = 10000000;
  }
}

Now i am going to interact with Truffle 1) I have done Truffle migrate

2) In Truffle console i used DappToken.deployed().then(function(i) {token = i ;})

3)deployed() returns a promise and then takes a call back (correct me if I am wrong )

4) Next i used

 token.totalSupply 
{ [Function]
  call: [Function],
  sendTransaction: [Function],
  request: [Function: bound ],
  estimateGas: [Function] }

// It is showing the following output

totalSupply is the name of the variable which i have given but it is showing Function in square brackets can any one explain how truffle is compiling inside and why it is showing me as Function I tried token.DappToken.totalSupply it is showing me error I thought it will go inside the contract and call the variable

Answer 1

Solidity do not expose variables directly, but it creates a public getter function.

Your example will behave like this.

contract DappToken {
  uint256 public _totalSupply;

  function DappToken () public {
    _totalSupply = 10000000;
  }
  function totalSupply() public view returns (uint256) {
    return _totalSupply;
  }
}

To get the total supply you have to make a call like regular function.

token.totalSupply().then((result) => { console.log(result); } )

Answer 2

Here is documentation. I think you need to call token.totalSupply inside then() similar to the example below:

var account_one = "0x1234..."; // an address

var meta;
MetaCoin.deployed().then(function(instance) {
  meta = instance;
  return meta.getBalance.call(account_one, {from: account_one});
}).then(function(balance) {
  // If this callback is called, the call was successfully executed.
  // Note that this returns immediately without any waiting.
  // Let's print the return value.
  console.log(balance.toNumber());
}).catch(function(e) {
  // There was an error! Handle it.
})