difference between “deploy” and “new”?

Question

So I'm using truffle and I notice that I seem to be able to deploy a contract's bytecode by calling deployer.deploy(MyContract);

But I've also seen people run:

myContract = await MyContract.new();

in a unit test without ever calling deployer.deploy().

Is my understanding correct? Do these bits of code do the same thing?

Thanks!

Answer 1

Both of the above functions are used to deploy the contract to the network.

deployer.deploy(myContract);

is used in our migration file.

We can deploy our own version to the network using the .new() function:

MetaCoin.new().then(function(instance) {

// do something

console.log(instance.address);

}).catch(function(err) {

// do something

});

Answer 2

They're both similar in that they deploy the contract. The difference is that .deploy() behaves like a singleton in that you can access the deployed instance with .deployed(). You typically use .new() in tests to avoid the possibility of any side-effects.

Here's an example:

Example.sol

pragma solidity ^0.4.23;

contract Example {
  uint256 public data;

  function set(uint256 _data) public {
    data = _data;
  }
}

Example.spec.js

const Example = artifacts.require('Example')

contract('Example', (accounts) => {
  let instance

  beforeEach('setup', async () => {
    instance = await Example.new()

    // second test will fail with `deployed()`
    //instance = await Example.deployed()
  })

  describe('test singleton', () => {
    it('should set data', async () => {
      assert.equal(await instance.data.call(), '0')
      const {receipt: {status}} = await instance.set(5)
      assert.equal(status, '0x01')
      assert.equal(await instance.data.call(), '5')
    })

    it('should not read previous data', async () => {
      // this will be `5` instead of `0` if using `deployed()`
      assert.equal(await instance.data.call(), '0')
    })
  })
})

Answer 3

I think the difference is that new() simply deploys a new instance of the contract. But when a contract is deployed by deployer.deploy(), the new instance is saved in the migration for later use with MyContract.deployed(), etc.