I have question about creating Struct where size of array passed to that struct could have different lengths. As in code below I could pass to this Recipe 2 ingredients, 3 ingredients or whatever amount if ingredients I would like with corresponding array of amounts.

Unfortunately I'm getting error:

TypeError: Invalid type for argument in function call. Invalid implicit conversion from uint8[2] memory to uint256[] memory requested.

I know that this comes from that I am passing fixed array size to dynamic array pole in Struct, what could be solution for that, if I want to be able to pass different sizes of arrays?

pragma solidity ^0.4.2;

contract Game {
    address public owner;

    // RECIPES
    mapping(uint256 => Recipe) private recipeInfo;

    struct Recipe {
        uint256 recipeId;
        uint256[] ingredientId;
        uint256[] ingredientAmount;
        uint256 ethCost;

    // constructor of game;
    function Game() public {
        owner = msg.sender;
        recipeInfo[1] = Recipe(1, [1, 5], [100, 100], 50000000);
        recipeInfo[2] = Recipe(2, [2, 3, 4], [100, 200, 300], 100000000);
  • have tried the explicit conversion ? uint256[]([1,5]) Apr 2, 2018 at 9:44
  • 1
    Yes I have tried: but Explicit type conversion not allowed from "uint256[2] memory" to "uint256[] memory"
    – Pacxiu
    Apr 2, 2018 at 11:46

1 Answer 1


From https://solidity.readthedocs.io/en/v0.4.21/types.html#array-literals-inline-arrays:

Note that currently, fixed size memory arrays cannot be assigned to dynamically-sized memory arrays, i.e. the following is not possible:

// This will not compile.

pragma solidity ^0.4.0;

contract C {
    function f() public {
        // The next line creates a type error because uint[3] memory
        // cannot be converted to uint[] memory.
        uint[] x = [uint(1), 3, 4];

It is planned to remove this restriction in the future but currently creates some complications because of how arrays are passed in the ABI.

For now, I suppose you'd have to do something like this:

uint256[] memory foo = new uint256[](2);
foo[0] = 1;
foo[1] = 5;
recipeInfo[1] = Recipe(1, foo, ...);
  • Hey, thanks. It worked. I was aware of that, fom solidity and couldn't get around it. Is this approach efficient in terms of gas cost?
    – Pacxiu
    Apr 2, 2018 at 11:34
  • I don't know, sorry.
    – user19510
    Apr 2, 2018 at 16:26

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