Platformio.ini variables

PlatformIO Core
1

The following works but is there anyway to do the C++ equivalent of “+=” to add to the variable instead of overwriting it?

[env:send]
extends = nanoatmega328new
build_flags =
    ${nanoatmega328new.build_flags}
    -D send_buildflag

I tried:

build_flags += -D send_buildflag

and even:

build_flags =
    ${this.build_flags}
    -D send_buildflag

but they both failed.