Enlarge the integral sign proportional to its content

Question

In LaTeX you have a command like \left(\right) to enlarge the brackets proportional to the content between the brackets.

for instance \left(a\right) will produce smaller brackets than \left(\displaystyle\frac{a}{b^n}\right)

Is there a similar trick for the integral sign?

Answer 1

A hacky solution using unicode-math that only works with fonts that have multiple integral sizes (e,g. Asana Math or Cambria Math), and xelatex or lualatex of course:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Asana Math}

\def\delint{\Udelimiter 4 \symoperators "222B }
\def\extint#1{\left\delint #1\right.}
\begin{document}
\[
\extint{\frac{\sum^{a+b}}{\sum_{x+y}}} \int
\]
\end{document}

Integral indices are broken, though (needs more thought).