why the C++ Mathematical Expression Library compiled so slow

[ztdep]

Dear friends:
I downloaded the C++ Mathematical Expression Library from the web, and i uploaded it in the attachment.
It consists of only one head file. But the compiling process is very slow under opensuse 42.3 with gcc. Could you please give me some advices for that.
Regards.

http://partow.net/programming/exprtk/index.html

[JLBorges]

> the compiling process is very slow under opensuse 42.3 with gcc

What is the version of the GNU compiler? Compiling this kind of code with older versions of g++ could be excruciatingly slow. (One reason is the exorbitant amount of memory that the compiler required for its internal data structures.)

[Thomas1965]

Since it is only 1 header file using pre-compiled header files would be option, though I am not sure if gcc supports this.