On Mon, 2024-01-22 at 21:33 -0500, Dmitry Goncharov wrote: > On Mon, Jan 22, 2024 at 8:16 AM Paul Smith <psm...@gnu.org> wrote: > > I don't understand the point you are making about +!=. > > If all new operators behave the same as +=, when the variable exists, > then +!= is not needed, because +!= would do the same as +=$(shell > ...).
They are not equivalent since if the variable is recursive the +!= model would execute the shell script immediately, one time, and append the result, while += $(shell ...) would re-run the shell script every time the variable was expanded. In addition to efficiency, it could be a noticeable behavior if the shell script does something (like list files or obtain a date or something) which might change between invocations. In other words in this situation: foo = bar foo +!= echo baz then the value of foo would be "bar baz", while in this situation: foo = bar foo += $(shell echo baz) the value of foo would be "bar $(shell echo baz)". Of course you can rewrite it to be the equivalent, like this: foo = bar __foo := $(shell echo baz) foo += $(__foo) here bar has a value of "bar $(__foo)": as long as __foo was not reset then it would give the same result as +!=. -- Paul D. Smith <psm...@gnu.org> Find some GNU Make tips at: https://www.gnu.org http://make.mad-scientist.net "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
