Xcode's Fix All in Scope
Xcode scans your code for compiler errors as you type. These errors show up as a red dot in the gutter that can be clicked to reveal the error message. Xcode may also provide a Fix-It that you can accept.
When your file contains multiple errors and you want to accept all the Fix-Its, do this: Editor > Fix All in Scope. Better yet, the keyboard shortcut: ctrl + opt + cmd + f.
This feature can be a little unpredictable because while Xcode does a great job of identifying compiler errors, it's not always great at suggesting fixes. But, when you're confident that you know what the fix is going to be, it can be very handy to let Xcode help you out.
One place I find myself using this feature is when I change my mind about a constant:
let foo = 1
// some code
foo += 1
I thought foo was going to be a constant, but then further down the file I realize my mistake - Xcode will error and I'm usually sure that hitting ctrl + opt + cmd + f will switch the let to var for me.