Variables

struct FacetAddressAndSelectorPosition {
        address facetAddress;
        uint16 selectorPosition;
    }

    struct DiamondStorage {
        // function selector => facet address and selector position in selectors array
        mapping(bytes4 => FacetAddressAndSelectorPosition) facetAddressAndSelectorPosition;
        bytes4[] selectors;
        // selectors => selectorAddress, selectorPostion(=selectorCount)
        mapping(bytes4 => bool) supportedInterfaces;
        // owner of the contract
        address contractOwner;
    }

Add

Main

// add the mapping value [selector => facetAdd, selectorCount]
ds.facetAdedressAndSelectorPosition[selector] 
= FacetAddressAndSelectorPosition(_facetAddress, selectorCount);

ds.selectors.**push**(selector); //  bytes4[] selectors;

// add the count of the selector
selectorCount++;

• code

Replace

change the address

ds.facetAddressAndSelectorPosition[selector].facetAddress = _facetAddress;

• code

Remove

// Input
(address _facetAddress, bytes4[] memory _functionSelectors)
// Example
(0xED98485593D5865E892f823e1f66FB99fE64F639, [0x12345678,0x456789ab])

// Methods

// _functionSelectors => selectorIndex 
bytes4 selector = _functionSelectors[selectorIndex];

// get the target selector and the its position and address
FacetAddressAndSelectorPosition memory **oldFacetAddressAndSelectorPosition** 
= ds.facetAddressAndSelectorPosition[selector];

// the target position to the last selector!
if (oldFacetAddressAndSelectorPosition.selectorPosition != selectorCount) {
    bytes4 lastSelector = ds.selectors[selectorCount];
    ds.selectors[oldFacetAddressAndSelectorPosition.selectorPosition] = lastSelector;
    ds.facetAddressAndSelectorPosition[lastSelector].selectorPosition = oldFacetAddressAndSelectorPosition.selectorPosition;
}

// delete
ds.selectors.pop(); // delete item of array
delete ds.facetAddressAndSelectorPosition[selector]; // delete item of  mapping

• code

https://piedao.notion.site/Upgradeable-Contracts-with-OZ-e1657f19c569475098a4ebf2a08a5d2b#41adefcce7a84882bd5bde01d8d79ae8