Structs.md

30 - Structs

They are custom defined types that can group several variables of same/different types together to create a custom data structure. The struct members are accessed using . e.g.: struct s {address user; uint256 amount} where s.user and s.amount access the struct members.

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Slide Screenshot

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Slide Deck

• Custom Data Structure
• Several Variables
• Different Types
• Struct Members -> . Access
• E.g.: s.user, s.amount
• Aggregate Type
• Commonly Used

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References

• Youtube Reference
• Solidity by Example - Structs

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Solidity by Example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.3;

contract Todos {
    struct Todo {
        string text;
        bool completed;
    }

    // An array of 'Todo' structs
    Todo[] public todos;

    function create(string memory _text) public {
        // 3 ways to initialize a struct
        // - calling it like a function
        todos.push(Todo(_text, false));

        // key value mapping
        todos.push(Todo({text: _text, completed: false}));

        // initialize an empty struct and then update it
        Todo memory todo;
        todo.text = _text;
        // todo.completed initialized to false

        todos.push(todo);
    }

    // Solidity automatically created a getter for 'todos' so
    // you don't actually need this function.
    function get(uint _index) public view returns (string memory text, bool completed) {
        Todo storage todo = todos[_index];
        return (todo.text, todo.completed);
    }

    // update text
    function update(uint _index, string memory _text) public {
        Todo storage todo = todos[_index];
        todo.text = _text;
    }

    // update completed
    function toggleCompleted(uint _index) public {
        Todo storage todo = todos[_index];
        todo.completed = !todo.completed;
    }
}