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04_storage.ipynb

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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "b52d942c",
+   "metadata": {},
+   "source": [
+    "# Storage"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6b581368",
+   "metadata": {},
+   "source": [
+    "The storage is a mapping from a `key` to a `value`. The number of keys is for all practical purposes infinite. The value can be up to 32 bytes. Every value is initialized with a 0.\n",
+    "\n",
+    "This is like the SSD in your computer. Storage is non-volatile."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "2a9d3e0b",
+   "metadata": {},
+   "source": [
+    "![title](static/storage.png)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f0d8d8db",
+   "metadata": {},
+   "source": [
+    "source: https://docs.alchemy.com/docs/smart-contract-storage-layout"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "0672532a",
+   "metadata": {},
+   "source": [
+    "We will represent the storage as a dictionary."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 50,
+   "id": "c5b98bfc",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class KeyValue:\n",
+    "    def __init__(self): self.storage = {}\n",
+    "    \n",
+    "    def load (self, key)       : return self.storage[key]\n",
+    "    def store(self, key, value): self.storage[key] = value"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "2e60b878",
+   "metadata": {},
+   "source": [
+    "### Warm/Cold"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "d7515c89",
+   "metadata": {},
+   "source": [
+    "It costs different amount of gas whether we access a warm or cold storage slot. \n",
+    "A slot is said to be `warm` if it was access before. Otherwise it is `cold`.\n",
+    "Accessing a slot that is `cold` costs more gas than accessing a `warm` slot.\n",
+    "\n",
+    "We implement that logic by keeping track of a `cache`. When we load a storage slot we save its key in that `cache`. If a key is in that `cache` it is said to be warm."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 43,
+   "id": "4d35c9ac",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class Storage(KeyValue):\n",
+    "    def __init__(self):\n",
+    "        super().__init__()\n",
+    "        self.cache = []\n",
+    "        \n",
+    "    def load(self, key):\n",
+    "        warm = True if key in self.cache else False\n",
+    "        if not warm: self.cache.append(key)\n",
+    "        if key not in self.storage: return 0x00\n",
+    "        return warm, super().load(key)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 44,
+   "id": "c9cba219",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "storage = Storage()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "352aa83d",
+   "metadata": {},
+   "source": [
+    "We store `420` in storage slot `1`"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 45,
+   "id": "4ff21851",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "storage.store(1, 420)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "037c7a05",
+   "metadata": {},
+   "source": [
+    "Notice how the first time retrieving something from storage slot `1` its `cold`"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 46,
+   "id": "7e3f84c7",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(False, 420)"
+      ]
+     },
+     "execution_count": 46,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "storage.load(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "80e548e3",
+   "metadata": {},
+   "source": [
+    "Now storage slot `1` is `warm`"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 47,
+   "id": "6c25d6ff",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(True, 420)"
+      ]
+     },
+     "execution_count": 47,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "storage.load(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "257055b8",
+   "metadata": {},
+   "source": [
+    "Reading a random storage that was not set to any value will return 0 and **not** throw an exception."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 51,
+   "id": "bc839596",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "0"
+      ]
+     },
+     "execution_count": 51,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "storage.load(42069)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}