library modifying string vs string literal

Question

I have a library which has the following function:

function strConcat(
    string memory _a,
    string memory _b
)
    internal pure
    returns (string memory)

My contract implements the library and uses the following:

using StringConverter for *;
...
uint minLevel = getStorageUint(
    r,
    ("_conf_").strConcat(pSetting),
    pSettingIndex,
    0
);

This is working, but if I change:

using StringConverter for string;

I can see the error:

TypeError: Member "strConcat" not found or not visible after argument-dependent lookup in literal_string "_conf_".
        ("_conf_").strConcat(pSetting),

What can I type at using to make it working correctly?

Answer 1

Try this solution:

First declare string variable:

string memory myVariable = "_conf_";

Then execute the concat.

myVariable.strConcat(pSetting);

I hope this works.

The problem you have comes arises, because

("_conf_").strConcat(pSetting)

doesn't explicitly create "_conf_" as a memory string.