The following Makefile: condset: COND ?= one condset: condset2 @echo $@ COND [$(COND)]
condset2: COND ?= two condset2: condset3 @echo $@ COND [$(COND)] condset3: COND ?= three condset3: @echo $@ COND [$(COND)] outputs: condset3 COND [three] condset2 COND [two] condset COND [one] I would have expected "one" in all cases. Note that: addset: COND += one addset: addset2 @echo $@ COND [$(COND)] addset2: COND += two addset2: addset3 @echo $@ COND [$(COND)] addset3: COND += three addset3: @echo $@ COND [$(COND)] produces: addset3 COND [one two three] addset2 COND [one two] addset COND [one] The reason I need such a construct falls out of another shortcoming I've run into while trying to use make to manage the configuration of a set of servers (basically a state machine): there's no way to specify a true ordering-only constraint in gmake's syntax. If there were a way to specify a weak dependency (e.g. if "A" and "B" are both targets under consideration, always complete "B" before "A" without any other side-effects) I wouldn't need the above. Unfortunately the order-only dependency cannot be used for this in a reusable way. In my case I'd like to have "init", "start" and "start_clean" end-user targets which reuse common targets which in turn depend on targets specified by the above semantic intent. If there were a true order-only operator (say ||), I could do: .PHONY: <all of the below> init_server: <some initialization for a running server> start_server: <start a server and load existing database info> start_clean_server: <start a server and create a clean database> common: || init_server start_server start_clean_server init: init_server common start: start_server common start_clean: start_server common If I try the above with the current order-only | operator all three dependencies are invoked by common. Is there a way to get the effect of the above that anyone can think of?
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