How to add requires in script mode?

[shaqtsui]

I need to install a package base on gcc version.
Detection api is not avialable in description scope, add require api is not available in scrip scope. (embarass face)

Try ask bing, got (for fun):

[waruqi]

use custom option + on_check to detect gcc version, then if has_config("optname") then add_requires in description scope.

[shaqtsui]

Nice trick :D