Is this really an improvement (moving var to inner scope when inner scope is in a loop)?

Question

ReSharper recommends that these vars:

List<string> senderDeviceIDList;
string senderDeviceID;
. . .
            foreach (var item in PlatypiIds)
            {
                senderDeviceIDList = await GetSenderDeviceIDForSenderID(item);
                senderDeviceID = senderDeviceIDList[0];

...can be declared in inner scope, like so:

    foreach (var item in PlatypiIds)
    {
        List<string> senderDeviceIDList = await GetSenderDeviceIDForSenderID(item);
        string senderDeviceID = senderDeviceIDList[0];

...but is that really "more better"? Doesn't that cause the vars to be declared N times (once for each foreach loop)?

Answer 1

There is no any benefit in terms of performance or memory allocation here, as variables inside or oustside of the if scope are declared in the IL, by the way.

The only benefit is localization of the variable scope. Move it to the scope where it's used, which brings goodness like:

• easy refactoring (may be the most important)

• readability. If you see variable inside the scope, you know that it's used only inside that scope and if you see some variable that apparently is not inside, you know that changing it can affect other parts of the code. So changing it introduce some potential danger.

In short, it's about readability and usability of the code you're writing and does not introduce any performance or memory consumption benefits.