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Solidity / Functions

internal function

Learn internal function in Solidity through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Beginner

internal function is an atomic Solidity topic inside Functions. This lesson focuses on how the internal function construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for internal function, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.

Topic-specific example

solidity-02-03-internal-function.sol
solidity Try It Live 
contract C { function _double(uint n) internal pure returns(uint){return n*2;} function run(uint n) external pure returns(uint){return _double(n);} }
Edge case / engineering note

For internal function, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

internal function Mastery Check →
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