simplify length()

9 jobs for halfedge-vector-and-length in 6 minutes and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #77855
VS2015
VS2015-32-bit

00:01:18

passed #77854
VS2015
VS2015-64-bit

00:01:26

passed #77853
VS2017
VS2017-32-bit

00:01:18

passed #77852
VS2015
VS2017-64-bit

00:01:33

passed #77849
Linux
clang-c++11

00:04:08

passed #77851
Linux
cppcheck

00:06:16

passed #77856
Linux
doc

00:00:32

passed #77848
Linux
gcc-c++11

00:02:19

passed #77850
Apple
macos-c++11

00:01:52