upgrade to c++20

Author: tomvanmele

setup.py

@@ -96,11 +96,11 @@ def has_flag(compiler, flagname):
 
 
 def cpp_flag(compiler):
-    """Return the -std=c++[11/14/17] compiler flag.
+    """Return the -std=c++[11/14/17/20] compiler flag.
 
     The newer version is prefered over c++11 (when it is available).
     """
-    flags = ["-std=c++14", "-std=c++11"]
+    flags = ["-std=c++20", "-std=c++17", "-std=c++14", "-std=c++11"]
 
     for flag in flags:
         if has_flag(compiler, flag):
@@ -113,7 +113,7 @@ class BuildExt(build_ext):
     """A custom build extension for adding compiler-specific options."""
 
     c_opts = {
-        "msvc": ["/EHsc", "/std:c++14"],
+        "msvc": ["/EHsc", "/std:c++20"],
         "unix": [],
     }
     l_opts = {