Alan Chan pinealan

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:

`vs` Questions

http://stackoverflow.com/questions/804115 (rebase vs merge).
https://www.atlassian.com/git/tutorials/merging-vs-rebasing (rebase vs merge)
https://www.atlassian.com/git/tutorials/undoing-changes/ (reset vs checkout vs revert)
http://stackoverflow.com/questions/2221658 (HEAD^ vs HEAD~) (See git rev-parse)
http://stackoverflow.com/questions/292357 (pull vs fetch)
http://stackoverflow.com/questions/39651 (stash vs branch)
http://stackoverflow.com/questions/8358035 (reset vs checkout vs revert)

Setting up a private ethereum blockchain for development and pointing your wallet at it

Ethereum tutorials all advise downloading the Mist wallet and beginning dev. The only problem is that the testnet and real blockchain are huge and take hours to download. What follows is a recipe for quickly setting up a small blockchain and pre-mining it with some test ethereum

The following is done in Linux but will work in MacOS and should have equivalent command line options in Windows. Where I don't give detailed instructions, it's because a quick google search will fill in the blanks.

Install geth https://github.com/ethereum/go-ethereum/wiki/geth

install Mist https://github.com/ethereum/mist/releases

README

The example below creates a TCP server listening on a stream (i.e. SOCK_STREAM) socket. A similar approach can be followed to create a UDP server on a datagram (i.e. SOCK_DGRAM) socket. See man systemd.socket for details.

An example server

Create an simple echo server at /opt/foo/serve.py.

	import datetime
	import hashlib
	import hmac
	import urllib.parse


	def aws_sig_v4_headers(access_key_id, secret_access_key, pre_auth_headers,
	service, region, host, method, path, query, payload):
	algorithm = 'AWS4-HMAC-SHA256'

	# The initial version
	if [ ! -f .env ]
	then
	export $(cat .env \| xargs)
	fi

	# My favorite from the comments. Thanks @richarddewit & others!
	set -a && source .env && set +a

	# http://webapps.stackexchange.com/questions/39587/view-estimated-size-of-github-repository-before-cloning
	# tested on macOS
	echo https://github.com/torvalds/linux.git \| perl -ne 'print $1 if m!([^/]+/[^/]+?)(?:\.git)?$!' \| xargs -I{} curl -s -k https://api.github.com/repos/'{}' \| grep size

	# output:
	# "size": 1746294,

	# After Ubuntu 16.04, Systemd becomes the default.
	# It is simpler than https://gist.github.com/Doowon/38910829898a6624ce4ed554f082c4dd

	[Unit]
	Description=Jupyter Notebook

	[Service]
	Type=simple
	PIDFile=/run/jupyter.pid
	ExecStart=/home/phil/Enthought/Canopy_64bit/User/bin/jupyter-notebook --config=/home/phil/.jupyter/jupyter_notebook_config.py

	# Hello, and welcome to makefile basics.
	#
	# You will learn why `make` is so great, and why, despite its "weird" syntax,
	# it is actually a highly expressive, efficient, and powerful way to build
	# programs.
	#
	# Once you're done here, go to
	# http://www.gnu.org/software/make/manual/make.html
	# to learn SOOOO much more.

	// Copyright (c) 2017 Ismael Celis

	// Permission is hereby granted, free of charge, to any person obtaining a copy
	// of this software and associated documentation files (the "Software"), to deal
	// in the Software without restriction, including without limitation the rights
	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	// copies of the Software, and to permit persons to whom the Software is
	// furnished to do so, subject to the following conditions:

	// The above copyright notice and this permission notice shall be included in all