Gas specification for function call

Question

Is it possible to specify gas cost for a particular function call? E.g. Let's say I want a transfer() function to cost 50000000 gas, would I be able to hardcode this into the function?

Answer 1

Are you asking how-to set the limit on a transaction, so that it will succeed if the contract requires 5m gas or less? If so, you can specify the limit in web3 as follows:

let tx = await myContract.methods.myMethod(params...).send({ gas: 5000000 })

Or maybe are you looking to ensure that a transaction consumes at least 5m gas? I'm not sure why you would want that but you could by adding a loop to the end of your function, something like:

function expensiveTransfer() public {
  uint maxGasLeft = gasleft();
  require(maxGasLeft > 5000000);
  maxGasLeft -= 5000000;

  ...normal function logic...

  while(gasleft() > maxGasLeft) {
    // wasting money till you spent enough
  }
}