[Ethereum] Splice Struct Entry by Index in Solidity

arrayscontract-developmentsoliditystruct

I have a struct and I'd like to remove an item by index:

struct Payout {
  address addr;
  uint yield;
}

Payout[] public payouts;

I'm not familiar with structs and more use to dealing with arrays in javascript where I would do something like this:

payouts.splice(index, 1);

What's the best way to do this with a struct array in Solidity?

Edit: Would also like array to shift down like with the splice function. E.g. when you delete payouts[0] the data from payouts[1] shifts back into its spot.

Best Answer

You can simply do:

function deletePayoutYield() {
    delete payout.yield;
}

Or in a array:

function deletePayoutYield(uint index) {
    delete payoutArray[index].yield;
}

function deletePayout(uint index) {
    delete payoutArray[index];
}

Related Solutions

Solidity Memory Management – Does ‘Delete’ Free Mapping Space

Based on my Debug observation:

I have tested that:

Firstly I insert data into my map data-structure as I explained in my question.
Secondly, I have returned the address of first mapped index, which is 0, this could be done for other indexes as well (0:10).
Without a delete operation I can retrieve the data perfectly fine from the address of mapped Foo[]. But if I did the delete operation, Solidity gives an error.

This debug result: leads me to conclude that memory is freed or address does not contain any valid information.

Test code:

set_txn_hash     = my_contract.transact().map_insert();
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)

for x in range(0, 9):
   for y in range(0, 9):
         output           = my_contract.call().get_(x, y);
         print(output);  //returns correct value.

set_txn_hash     = my_contract.transact().map_remove_map();                                             
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)                                      

set_txn_hash     = my_contract.transact().get_map_address(0);
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)

output           = my_contract.call().get_map();
print(output);

output           = my_contract.call().try_();
print(output);  //Solidity gives error if delete map_remove_map() is called

Additional functions inside my Contract:

  function map_insert(){
    for(uint i = 0; i < 10; i++)
      for(uint j = 0; j < 10; j++)
        add(i, i*10 + j);
  }

  function map_remove_map(){
    for(uint i = 0; i < 10; i++)
      delete_(i);
  }

  function map_remove_map_item(){
    for(uint i = 0; i < 10; i++)
      for(uint j = 0; j < 10; j++)
        delete_items(i, j);
  }

  function get_map_address(uint id) {
    uint addr;
    Foo[] a = foo[id];

    assembly{
    addr := a
        }
    map_address = addr;
  }

  function get_map() constant returns (uint){
    return map_address;
  }

  function try_() constant returns (uint ){
    uint addr = map_address;
    Foo[] a;
    assembly{
    a := addr
        }
    return a[1].x;  
  }

Solidity Arrays – Inserting Objects at Specified Position

There is no built-in method for inserting a value at a specific position in an array. You'll just have to write a loop to do it.

If you're going to be inserting a lot of elements in the middle of the array, it may make more sense to use a linked list instead of an array, so that you aren't doing as many storage writes, which can be expensive.

Best Answer

Related Solutions

Solidity Memory Management – Does ‘Delete’ Free Mapping Space

Solidity Arrays – Inserting Objects at Specified Position

Related Topic