Licenses

In Solidity, the SPDX (Software Package Data Exchange) license identifier is a way to specify the license under which a smart contract or library is distributed. This identifier is a short string that represents a specific open-source license, such as "MIT" for the MIT License or "GPL-3.0" for the GNU General Public License version 3.0.

The SPDX license identifier is used in the Solidity contract or library source code, usually in a comment at the top of the file. For example, to specify that a contract is distributed under the MIT License, the developer would add the following comment at the top of the contract source code:

// SPDX-License-Identifier: MIT

This helps to make it clear which open-source license applies to the code and makes it easier for users of the code to understand the legal terms under which they can use it.

It's important to note that the use of SPDX license identifiers is optional and not mandatory, but it is a best practice for Open Source projects to use it for clarity and compliance.

Pragma

In the Solidity programming language, a "pragma" is a compiler directive that provides information to the compiler about how to process the code. It is used to specify the version of Solidity that the code is written in and any other compiler-specific options that may be required.

The pragma statement is usually the first line of code in a Solidity file and it looks like this:

pragma solidity ^0.8.0;

In this example, "pragma solidity" is the directive and "^0.8.0" is the version number. The caret symbol (^) means that the code is written for version 0.8.0 or higher.

By using pragma solidity version you can ensure that the smart contract will be compatible with the compiler version.

It's important to note that pragma is not a keyword and can only be used for the purpose of specifying the compiler version.