How to match double stem in target like %/% or other way?

Question

I need to build targets with names like,

v1/thread4/foo  v1/thread8/foo v1/thread16/foo
v2/thread4/foo  v2/thread8/foo v2/thread16/foo

I want

Answer 1

It's pretty easy when you realise that $@ is v1/thread4/foo (say), to then pull out the bits you need.

In this case, something like:

v = $(firstword $(subst /, ,$@))
thread = $(notdir ${@D})

YMMV of course. leading to

targets := \
  v1/thread4/foo v1/thread8/foo v1/thread16/foo \
  v2/thread4/foo v2/thread8/foo v2/thread16/foo

all: ${targets}

v = $(firstword $(subst /, ,$@))
thread = $(notdir ${@D})

${targets}:
    : '$@: v [$v] thread [${thread}]'

giving

$ make
: 'v1/thread4/foo: v [v1] thread [thread4]'
: 'v1/thread8/foo: v [v1] thread [thread8]'
: 'v1/thread16/foo: v [v1] thread [thread16]'
: 'v2/thread4/foo: v [v2] thread [thread4]'
: 'v2/thread8/foo: v [v2] thread [thread8]'
: 'v2/thread16/foo: v [v2] thread [thread16]'