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Variable Assignment
-------------------
Variable definitions are parsed as follows:
IMMEDIATE = DEFERRED
IMMEDIATE ?= DEFERRED
IMMEDIATE := IMMEDIATE
IMMEDIATE += DEFERRED or IMMEDIATE
define IMMEDIATE
DEFERRED
endef
define IMMEDIATE =
DEFERRED
endef
define IMMEDIATE ?=
DEFERRED
endef
define IMMEDIATE :=
IMMEDIATE
endef
define IMMEDIATE +=
DEFERRED or IMMEDIATE
endef
For the append operator, `+=', the right-hand side is considered
immediate if the variable was previously set as a simple variable
(`:='), and deferred otherwise.
复制代码
变量定义被如下解析：
IMMEDIATE = DEFERRED
IMMEDIATE ?= DEFERRED
IMMEDIATE := IMMEDIATE
IMMEDIATE += DEFERRED or IMMEDIATE
define IMMEDIATE
DEFERRED
endef
define IMMEDIATE =
DEFERRED
endef
define IMMEDIATE ?=
DEFERRED
endef
define IMMEDIATE :=
IMMEDIATE
endef
define IMMEDIATE +=
DEFERRED or IMMEDIATE
endef
For the append operator, `+=', the right-hand side is considered
immediate if the variable was previously set as a simple variable
(`:='), and deferred otherwise.
对于连接符号 +=， 如果变量已经被定义为一个简单变量(:=)，那么右手边就被认为是立即性的，
否则就是推迟性的。
后文待续
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/09/17/2688335.html，如需转载请自行联系原作者
