How to store a large mapping in a smart contract?

Question

I have a contract that need to access the address of different tokens given their name as a string. I thought about doing the below:

contract MyContract{
     mapping (string => address) public tokens;
     constructor() {
         setUpTokens();
     }

     function setUpTokens() public {
        tokens["DAI"] = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
        tokens["USDC"] = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;
        tokens["USDT"] = 0xdAC17F958D2ee523a2206206994597C13D831ec7;
        tokens["BUSD"] = 0x4Fabb145d64652a948d72533023f6E7A623C7C53;
        ...
    }

}

I am trying to understand:

1/ how will this be stored?

2/ is the best way to achieve access to such a mapping from my contract. And if not how?

Answer 1

That's probably the way to go. Another way could be to just set them all as constants though (just hardcoded from deployment). If you're not going to change them, reading them later could make it cheaper than looking it up in a mapping

Answer 2

1/ how will this be stored?

tokens["DAI","USDT","aakash"] = [0x6B17..., 0xA0b8...., 0xD2ee52...];

2/ best way to achieve access to such a mapping from my contract. And if not how?

to access the tokens[] you need two things:

1. Solidity function: e.g.

function getTokenAddress(string memory TokenName) public view returns(address){
    return tokens[TokenName];
}

2. Call solidity functions with your favorate programming language. e.g. use modules web3JS, ether, etc. Use call() & send() functions to interact with smart contract. take reference from docs: https://web3js.readthedocs.io/en/v1.7.3/web3-eth-contract.html

To upgrade your smart contract, add 2 more functions:-

1. function to rewrite & add new address for a tokenName:

function addToken(string memory TokenName,address TokenAddress) public {
    tokens[TokenName]=TokenAddress;
}

2. function to Delete Token and Address:

function deleteTokenAndAddress(string memory TokenName) public{
   delete tokens[TokenName];
}

Complete correct solidity codes:-

//SPDX-License-Identifier: MIT
pragma solidity >0.8.0 <0.9.0;
contract calculate{
    mapping (string => address) public tokens;

    constructor() {
         setUpTokens();
    }

    function setUpTokens() public {
        tokens["DAI"] = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
        tokens["USDC"] = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;
        tokens["USDT"] = 0xdAC17F958D2ee523a2206206994597C13D831ec7;
        tokens["BUSD"] = 0x4Fabb145d64652a948d72533023f6E7A623C7C53;
    }

    // eg. getTokenAddress("DAI") will return DAI address above
    function getTokenAddress(string memory TokenName) public view returns(address){
        return tokens[TokenName];
    }

    function addToken(string memory TokenName,address TokenAddress) public {
        tokens[TokenName]=TokenAddress;
    }

    function deleteTokenAndAddress(string memory TokenName) public{
        delete tokens[TokenName];
    }
}