Merge pull request #159 from shikhar360/variablevisibility

Visibility of state variable section added

Author: 7i7o

lessons/projects/1.mdx

@@ -284,6 +284,24 @@ contract WAGMI {
         - **Struct:** Solidity allows users to create and define their own type in the form of structures. The structure is a group of different types even though it’s not possible to contain a member of its own type. The structure is a reference type variable which can contain both value types and reference types.
     - **Mapping Type**: Stores the data in a key-value pair where a key can be any value types. It is like a hash table or dictionary as in any other programming language, where data can be retrieved by key.
 
+    ### Visibility of State Variables
+
+    In Solidity , there are 3 types of variable visibility modifiers that a developer can use :
+
+    - **Public**: If a state variable visibility is marked as `public` then those variables can be used within the smart contract and can be accessed by other contracts as well. Compilers automatically generates functions to read its value when calling the contract, they are called 'getter' functions.
+
+    - **Internal**: A state variable with an `internal` visibility can only be accessed within the smart contract and its derived contracts. It can *NOT* be accessed externally. This is the default for state variables when no visibilty is specified.
+
+    - **Private**: When a state variable visibility is marked as `private` it is only meant to be used within the defined smart contract . No derived contract can read a variable with a `private` visibility.
+
+    <ContentCallout emoji='💡' size='md' variant='info'>
+    While private and internal are not readable or modifiable from other contracts, its values are set on a public blockchain, making its values visible from the outside world.
+    </ContentCallout>
+ 
+    #### Which visibility should I use ?
+
+    A simple answer to this is , start with giving every variable a `private` visibility then as you move further in contract developement modify variables to `internal` visibility as a next step of modification. Try to use `public` visibility as little as possible in order to be gas efficient and making less vulnerabilities in the smart contract.
+
 </ContentSideDrawer>
 
 ## Creating Functions
@@ -689,8 +707,7 @@ you see the magical spell that is being cast here?
 Before you go ahead and tell us: **what your future in web3 is,** have a check
 on what you didn’t know a little while ago, and what you know now! *
 
-Apart from a user wallet, what else uses a blockchain (Ethereum)
-address?
+Apart from a user wallet, what else uses a blockchain (Ethereum) address?
 
 How many parameters can we have in an event?
 
@@ -700,8 +717,7 @@ Ethereum uses something for transaction fees. What’s it called?
 
 Where do the values for event parameters get stored?
 
-What is the use of the **pragma solidity** statement in our smart
-contract?
+What is the use of the **pragma solidity** statement in our smart contract?
 
 Do state variables stay permanently on the blockchain?
 
@@ -710,4 +726,4 @@ Can a view function modify the state of the blockchain?
 What can we use a smart contract for?
 
 **Now, go to the community in Discord to share your new Open Sourcerer
-powers**......and find the answers too!!! 
+powers**......and find the answers too!!!