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Answers to Deep Questions about Solidity

The following list of questions was taken from https://www.reddit.com/r/ethereum/comments/72reba/do_you_have_deep_questions_about_solidity_or_the/

An updated summary on the different ways one could have two contracts interact (DELEGATECALL, STATICCALL, libraries, all that stuff) with clear pros/cons for each (gas cost, whether it requires EVM assembly directives, etc)

Question by /u/drcode

I won't talk about low-level opcodes here because of the brevity of the answer. In general, there are four ways functions can be called in Solidity:

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    def __init__(self, dataStoreContractAddress, contractAbiFile):
        with open(contractAbiFile, 'r') as abi_definition:
            self.abi = json.load(abi_definition)
        self.dataStoreContractAddress = dataStoreContractAddress
        self.w3 = Web3(IPCProvider('/home/a/.ethereum/geth.ipc'))
        self.w3_contract = self.w3.eth.contract(self.abi, self.dataStoreContractAddress) 

bonedaddy

pragma solidity 0.4.18;

// implement safemath as a library
library SafeMath {

  // We use `pure` bbecause it promises that the value for the function depends ONLY
  // on the function arguments
  function mul(uint256 a, uint256 b) internal pure  returns (uint256) {
    uint256 c = a * b;
    require(a == 0 || c / a == b);

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To generate random numbers for your contract you must provide the contract with the following interface

interface RandomNumberGeneratorInterface 
    function getRandomNumber(uint256 _max) public returns (uint256);
}

Example of how you would use it with a contract

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pragma solidity ^0.4.0;
import "github.com/oraclize/ethereum-api/oraclizeAPI.sol";

contract YoutubeViews is usingOraclize {
    
    uint256 public  ethUSD;
    
    mapping (bytes32 => bool) public validOraclizeIds;
    
    event newOraclizeQuery(string description);

bonedaddy

pragma solidity ^0.4.0;
import "github.com/oraclize/ethereum-api/oraclizeAPI.sol";

contract lol is usingOraclize {
    
    uint public DieselPriceUSD;

    event newOraclizeQuery(string description);
    event newDieselPrice(string price);
    

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pragma solidity 0.4.19;

import "./Modules/Oraclize.sol";


contract test is usingOraclize {


	uint256 public ethUSD;

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pragma solidity 0.4.19;

import "./Modules/Oraclize.sol";


contract test is usingOraclize {


	uint256 public ethUSD;

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pragma solidity 0.4.19;

import "./Modules/Oraclize.sol";


contract test is usingOraclize {


	uint256 public ethUSD;

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package main

import (
	"fmt"
	//"strings"
	"net/http"
	"io/ioutil"
	"log"
	"encoding/json"
)