1# $NetBSD: counter-append.mk,v 1.5 2021/04/04 10:13:09 rillig Exp $ 2# 3# Demonstrates how to let make count the number of times a variable 4# is actually accessed, using the ::+= variable modifier. 5# 6# This works since 2020-09-23. Before that, the counter ended up at having 7# 6 words, even though the NEXT variable was only accessed 3 times. 8# The cause for this surprising behavior was that the ::= variable modifiers 9# returned an error marker instead of a simple empty string. 10 11RELEVANT= yes (load-time part) # just to filter the output 12 13COUNTER= # zero 14 15NEXT= ${COUNTER::+=a}${COUNTER:[#]} 16 17# This variable is first set to empty and then expanded. 18# See parse.c, function Parse_Var, keyword "!Var_Exists". 19A:= ${NEXT} 20B:= ${NEXT} 21C:= ${NEXT} 22 23RELEVANT= no 24 25all: 26 @: ${RELEVANT::=yes (run-time part)} 27 @echo A=${A:Q} B=${B:Q} C=${C:Q} COUNTER=${COUNTER:[#]:Q} 28 @: ${RELEVANT::=no} 29