[Ethereum] Delete all elements from an array

solidity

I am writing a smart contract to be the backend of a game. Instead of using a mapping, I have decided to use an array to store the addresses of accounts who have paid my contract. (I know it is common practice to use a mapping for this but I find them to be confusing)

address[] paidPlayers;

As players join, their address is added via the following function.

function addPlayer(address player) constant returns (address[]) {
   paidPlayers.push(player);
   return paidPlayers;
}

Periodically, when a round in the game is completed, I want my contract to reset. I thus need a way of emptying my paidPlayers array. How is this done in solidity? Is there anything like the javascript

paidPlayers = [];

I have found methods for deleting a specific element but not the array as a whole.

Best Answer

From Solidity Documentation Tips and Tricks

Use delete on arrays to delete all its elements.

delete paidPlayers;

This is exactly the same as paidPlayers.length = 0

Related Solutions

[Ethereum] How to properly delete array elements

There is more too this than meets the eye.

First, there is no way to truly delete since the transaction that created the element and the previous states of the chain will forever remain part of immutible history.

Second, although it will help reduce chain bloat by marking the storage as useless (in the present state), the delete operation is in fact unavoidably a write to the state which costs gas to execute.

Third, logically deleting an element doesn't reorganize the list. It merely creates a void in the midst of the list, roughly like [a,b,c, nothing, e,f,g]. This _might) create logical problems in or around the contract.

A reorganization is possible in the case of an unordered list. This is done by moving the last element in the list into the slot to delete and then reducing the length of the array. This only works with "unordered" lists because it relies on shuffling the order of the elements. https://medium.com/@robhitchens/solidity-crud-part-2-ed8d8b4f74ec

You may find that either leaving the elements in place or reorganizing around mappings is actually a better data structure. You can also consider a soft delete which admittedly does nothing to reduce chain bloat.

Have a look over here for a mapped struct with delete pattern. Are there well-solved and simple storage patterns for Solidity?

Hope it helps.

UPDATE:

Thanks, smarx, for jumping in. Now, I'm curious!

Is it wrong to think delete is always a net costly operation?

pragma solidity ^0.4.20;

contract Refunds {

    mapping(uint => bool) public data;

    function setIt() public {
        data[1] = true;
    }

    function deleteIt() public {  // net cost ~ 5000 gas
        delete data[1];
    }
}

Best Answer

Related Solutions

[Ethereum] How to properly delete array elements

Related Topic