SPDX license and pragma version in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the SPDX license identifier in a Solidity file?

The SPDX license identifier specifies the license under which the Solidity code is released. It helps tools and users understand the legal terms quickly.

beginner

Where should the SPDX license identifier be placed in a Solidity file?

It should be placed as the very first line in the Solidity file, starting with // SPDX-License-Identifier: followed by the license type.

beginner

What does the pragma version statement do in Solidity?

The pragma version statement tells the compiler which versions of Solidity the code is compatible with, ensuring the code compiles correctly.

intermediate

Explain the difference between pragma solidity ^0.8.0; and pragma solidity 0.8.0;.

pragma solidity ^0.8.0; means the code works with version 0.8.0 and any newer 0.8.x versions but not 0.9.0 or above. pragma solidity 0.8.0; means it only works with exactly version 0.8.0.

intermediate

Why is it important to specify both SPDX license and pragma version in Solidity files?

Specifying SPDX license clarifies legal usage rights, and pragma version ensures the code compiles with the intended compiler version, preventing errors and misunderstandings.

What is the correct way to specify an MIT license in a Solidity file?

A // SPDX-License-Identifier: MIT

B // License: MIT

C pragma license MIT;

D license MIT;

The SPDX license identifier must be written as a comment starting with // SPDX-License-Identifier: followed by the license name.

What does pragma solidity ^0.8.0; mean?

A Compatible with Solidity version 0.8.0 and above, but less than 0.9.0

B Compatible only with Solidity version 0.8.0

C Compatible with any Solidity version

D Compatible with Solidity versions below 0.8.0

The caret (^) means any version from 0.8.0 up to but not including 0.9.0.

Where should the pragma version statement be placed in a Solidity file?

A Inside the contract functions

B Anywhere in the contract code

C At the very end of the file

D After the SPDX license identifier and before the contract code

The pragma statement should be near the top, after the SPDX license line, to tell the compiler which version to use.

What happens if you omit the SPDX license identifier in your Solidity file?

A The code will automatically be licensed under MIT

B The compiler will throw an error and refuse to compile

C There is no legal information about the code license, which may cause confusion

D The pragma version will be ignored

Omitting SPDX means no license info is declared, which can cause legal uncertainty.

Which of the following is a valid SPDX license identifier?

A GPLv3

B GPL-3.0-or-later

C GNU Public License 3

D GPL version 3

SPDX license identifiers follow a specific format like GPL-3.0-or-later.

Describe the role of the SPDX license identifier and where it should be placed in a Solidity file.

Think about legal clarity and file structure.

Explain how the pragma version statement controls which Solidity compiler versions can compile your code.

Consider compatibility and preventing errors.