What's the code for “evaluated at” line with separate limits?

Question

I want the limits separated, like in the second one here:

• TOO CLOSE: $\int_{a}^{b}$
• RIGHT: $\int\limits_{a}^{b}$

How to I do the same thing with the vertical line "evaluated at"-limits?

• TOO CLOSE: $|_{a}^{b}$ then the limits are too close; I want them
  more separated.
• RIGHT: ???

Answer 1

Some of the usual options are to use some \vphantom or just making the symbol larger.

\documentclass{article}
\begin{document}
\begin{itemize}
 \item $|_{a}^{b}$ WRONG?
 \item ${|\vphantom{\big|}}_{a}^{b}$ BETTER?
 \item $\Big|_{a}^{b}$ BETTER?
\end{itemize}
\end{document}

Of course, you can also work with $\left. <some stuff> \right|_{a}^{b}$.