🍣 add some boilerplates

master_solidity/boilerplates/hello-world.sol

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+// Specifies the version of Solidity, using semantic versioning.
+// Learn more: https://solidity.readthedocs.io/en/v0.5.10/layout-of-source-files.html#pragma
+pragma solidity ^0.5.10;
+
+// Defines a contract named `HelloWorld`.
+// A contract is a collection of functions and data (its state).
+// Once deployed, a contract resides at a specific address on the Ethereum blockchain.
+// Learn more: https://solidity.readthedocs.io/en/v0.5.10/structure-of-a-contract.html
+contract HelloWorld {
+
+    // Declares a state variable `message` of type `string`.
+    // State variables are variables whose values are permanently stored in contract storage.
+    // The keyword `public` makes variables accessible from outside a contract
+    // and creates a function that other contracts or clients can call to access the value.
+    string public message;
+
+    // Similar to many class-based object-oriented languages, a constructor is
+    // a special function that is only executed upon contract creation.
+    // Constructors are used to initialize the contract's data.
+    // Learn more: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#constructors
+    constructor(string memory initMessage) public {
+        // Accepts a string argument `initMessage` and sets the value
+        // into the contract's `message` storage variable).
+        message = initMessage;
+    }
+
+    // A public function that accepts a string argument
+    // and updates the `message` storage variable.
+    function update(string memory newMessage) public {
+        message = newMessage;
+    }
+}