Swift 2 unused constant warning

问题

I am getting a warning saying my constant is unused:

Initialization of immutable value 'myConst' was never used; consider replacing with assignment to '_' or removing it

if someVal["value"] != nil {
    let myConst = someVal["value"]
}

So what will renaming let myConst = someVal["value"] into _ myConst = someVal["value"] do/mean?

回答1:

You're not replacing let with _, but you're replacing the variable name with it. If the variable isn't used anywhere in the code it's irrelevant so the line can be written like:

_ = someVal["value"]

If you want to use it somewhere you need a name for it to reference it later on. But when you don't use it writing _ is a lot easier ...

回答2:

we can use Wildcard Pattern ' _ ' for unused constant warings

回答3:

If you are never using it there is no need for the compiler to use let/var variable_name. So do not replace it with _ if you mean to use it later.