1# $NetBSD: cond-late.mk,v 1.6 2023/12/10 20:12:28 rillig Exp $ 2# 3# Using the :? modifier, expressions can contain conditional 4# expressions that are evaluated late, at expansion time. 5# 6# Any expressions appearing in these conditions are expanded before parsing 7# the condition. This is different from conditions in .if directives, where 8# expressions are evaluated individually and only as far as necessary, see 9# cond-short.mk. 10# 11# Because of this, variables that are used in these lazy conditions 12# should not contain double-quotes, or the parser will probably fail. 13# 14# They should also not contain operators like == or <, since these are 15# actually interpreted as these operators. This is demonstrated below. 16# 17 18all: cond-literal 19 20COND.true= "yes" == "yes" 21COND.false= "yes" != "yes" 22 23# If the order of evaluation were to change to first parse the condition 24# and then expand the variables, the output would change from the 25# current "yes no" to "yes yes", since both variables are non-empty. 26# expect: yes 27# expect: no 28cond-literal: 29 @echo ${ ${COND.true} :?yes:no} 30 @echo ${ ${COND.false} :?yes:no} 31 32VAR= ${${UNDEF} != "no":?:} 33# expect-reset 34# expect: make: Bad conditional expression ' != "no"' before '?:' 35.if empty(VAR:Mpattern) 36.endif 37