Can not choose clang version on FreeBSD

[fasxmut]

Commonly there are several different versions of clang installed on the FreeBSD system, but b2 seems can only use the default clang:

This works:
b2 toolset=clang

This works:
using clang ;

But these all fail:
b2 toolset=clang10
b2 toolset=clang-10
b2 toolset=clang11
b2 toolset=clang-11
b2 toolset=clang-devel

using clang : 10 ;

using clang : 11 ;

using clang : devel ;

It just can not use alt clang except the default.
If I try them and find,
b2 toolset=clang-11 -n
gives me screen information that it still invokes clang++,
the real c++ compiler command should be clang++11

[fasxmut]

After two days I have to reply my own question, because I got the answer by myself.
When I read toolset.jam and clang.jam I got a bunch of arg variables $(2), $(3), ..., $(9), they are not so easy to understand whats the meaning. But Finally I got something. There is a way but it is not perfect, write it at the top of the project Jamfile :

using clang : 11 : clang++11 ;

The second arg (11) passed to using can be anything, but do not include dash - , and the extra fourth args can be used:

using clang : 11 : clang++11 : <cxxflags>-std=c++20 ;
using clang : 10 : clang++10 ;

Here it is ok to only type command b2, but command b2 toolset=clang-11 will cause it to report duplicate error.

[stale]

Thank you for your contributions. Main development of B2 has moved to https://github.com/bfgroup/b2
This issue has been automatically marked as "transition" to indicate the potential for needing transition to the new B2 development project.