Solidity Arrays – Inserting Objects at Specified Position

arrayssolidity

I have following code piece:

  struct PaymentReceipt{
    uint   start_block;
    uint   end_block;
  }
  PaymentReceipt[] paymentReceiptList;

  function verfiyPayment(uint block_start, uint block_end) returns (bool success) {
    paymentReceiptList.push(PaymentReceipt({start_block: block_start, end_block: block_end }));
    return true;
  }

As I know, each new Struct will be pushed on top of the stack, so latest element (paymentReceiptList.length) will always point to the latest pushed Struct.

https://github.com/ethereum/wiki/wiki/Solidity-Features:

Dynamically-sized storage arrays have a member function push, such
that var l = arr.push(el); is equivalent to arr[arr.length++] = el;
var l = arr.length;.

For example, Java has following approach that: we can insert the specific element at the specified position in the list.

[Q] Is it possible to push an object into an Array with a given index and shift indexes, like the example on Java?

Best Answer

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.

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;  
  }

[Ethereum] Accessing to a dynamically sized array value in a contract

The issue is that the RPC keccak is actually slightly different than the one used in Solidiy. To get hashes consistent with solidity, use the ethereumjs-abi library. For example:

var abi = require('ethereumjs-abi')
var BN = require('bn.js')

abi.soliditySHA3(
    ["uint"],
    [ new BN(1)]
).toString('hex')

> "b10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6"

This is the correct hash that you should use. Also, be sure to pass in the actual hex value to getStorageAt, i.e. by passing in the result of abi.soliditySHA3 without converting to a hex string.

Best Answer

Related Solutions

Solidity Memory Management – Does ‘Delete’ Free Mapping Space

[Ethereum] Accessing to a dynamically sized array value in a contract

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