using mappings inside structs

Question

I'm trying to use a mapping inside a struct:

struct PoolStruct {
    uint currentUserID;
    uint activeUserID;
    uint price;
    uint minimalReferrals;
    mapping(uint => address) poolUserList;
  }

the code compiles, so i guess it's somehow permitted. The problem starts when i try to assign to that property:

PoolStruct memory pool;
pool = PoolStruct({
  currentUserID: 1,
  activeUserID: 1,
  price: POOL_PRICES[i],
  minimalReferrals: POOL_MINIMAL_REFERRALS[i]
});
pool.poolUserList[1] = msg.sender;

get an error on the last line...

TypeError: Member "poolUserList" is not available in struct Definitions.PoolStruct memory outside of storage.
       pool.poolUserList[currUserID] = msg.sender;
       ^---------------^

Is there any way to make this work?

@goodvibration, i edited the question with the error. currUserID is a uint (1) — André Alçada Padez, Jul 01 '20 at 13:24
Yeah, well, you can use mapping only in storage (i.e., non-local) variables. So the same goes for a struct which holds a mapping. — goodvibration, Jul 01 '20 at 13:29
You probably wanna take that mapping outside the PoolStruct structure, and redefine it as mapping(uint => PoolStruct) poolUserList. — goodvibration, Jul 01 '20 at 13:30

score 14 · Answer 1 · answered Jul 12 '20 at 16:52

14

The problem is that mappings can only live in storage. When you define PoolStruct memory pool;, the mapping member cannot be created in memory, and therefore the memory struct should be treated as if the mapping member never existed (for solidity < 0.7.0).

Starting from solidity 0.7.0, the line PoolStruct memory pool will produce an error saying that structs containing (nested) mappings must have storage as data location.

answered Jul 12 '20 at 16:52

hrkrshnn

426
3
9

@hrkshnn, Then, how should I declare? 'PoolStruct storage pool' also seems to throw an error. Saying 'Struct containing a (nested) mapping cannot be constructed.' – Sang-hoon Shin Sep 14 '20 at 16:14
@Sang-hoon-Shin what does the error say? – hrkrshnn Sep 14 '20 at 16:16
It says "Struct containing a (nested) mapping cannot be constructed" – Sang-hoon Shin Sep 14 '20 at 16:23
Please check my question: https://ethereum.stackexchange.com/questions/87451/solidity-error-struct-containing-a-nested-mapping-cannot-be-constructed – Sang-hoon Shin Sep 14 '20 at 16:24

score 0 · Answer 2 · answered Sep 17 '21 at 16:36

0

Just keep the mapping outside the struct. you do not have to keep inside the struct

     mapping(uint => address) poolUserList;

answered Sep 17 '21 at 16:36

Yilmaz

1,580
10
24

score 0 · Answer 3 · answered Mar 04 '22 at 14:27

0

A mapping can only be returned in a struct in a function, if the function is internal or when using a library.

answered Mar 04 '22 at 14:27

nathan nnamdi

1

using mappings inside structs

3 Answers3

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