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authorChris Larson <chris_larson@mentor.com>2010-02-25 16:42:28 (GMT)
committerRichard Purdie <rpurdie@linux.intel.com>2010-03-22 15:02:59 (GMT)
commit57044b9a6240235a403eac4067e2e2113e03b6eb (patch)
tree46f15cb768778aa0f8363d6da2e98c6aaa69aadb /bitbake/doc
parentada2a8494a88b59de25c0a44fce30190f560eff4 (diff)
downloadpoky-57044b9a6240235a403eac4067e2e2113e03b6eb.tar.gz
Implement ??= operator
??= is a lazy, conditional assignment. Whereas a ?= immediately assigns to the variable if the variable has not yet been set, ??= does not apply the default assignment until the end of the parse. As a result, the final ??= for a given variable is used, as opposed to the first as in ?=. Note that the initial implementation relies upon finalise() to apply the defaults, so a "bitbake -e" without specifying a recipe will not show the defaults as set by ??=. Moving application of the default into getVar adds too large a performance hit. We may want to revisit this later. (Bitbake rev: 74f50fbca194c9c72bd2a540f4b9de458cb08e2d) Signed-off-by: Chris Larson <chris_larson@mentor.com> Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>
Diffstat (limited to 'bitbake/doc')
-rw-r--r--bitbake/doc/manual/usermanual.xml8
1 files changed, 7 insertions, 1 deletions
diff --git a/bitbake/doc/manual/usermanual.xml b/bitbake/doc/manual/usermanual.xml
index c340344..450ac77 100644
--- a/bitbake/doc/manual/usermanual.xml
+++ b/bitbake/doc/manual/usermanual.xml
@@ -91,7 +91,13 @@ share common metadata between many packages.</para></listitem>
91 <section> 91 <section>
92 <title>Setting a default value (?=)</title> 92 <title>Setting a default value (?=)</title>
93 <para><screen><varname>A</varname> ?= "aval"</screen></para> 93 <para><screen><varname>A</varname> ?= "aval"</screen></para>
94 <para>If <varname>A</varname> is set before the above is called, it will retain it's previous value. If <varname>A</varname> is unset prior to the above call, <varname>A</varname> will be set to <literal>aval</literal>.</para> 94 <para>If <varname>A</varname> is set before the above is called, it will retain it's previous value. If <varname>A</varname> is unset prior to the above call, <varname>A</varname> will be set to <literal>aval</literal>. Note that this assignment is immediate, so if there are multiple ?= assignments to a single variable, the first of those will be used.</para>
95 </section>
96 <section>
97 <title>Setting a default value (??=)</title>
98 <para><screen><varname>A</varname> ??= "somevalue"</screen></para>
99 <para><screen><varname>A</varname> ??= "someothervalue"</screen></para>
100 <para>If <varname>A</varname> is set before the above, it will retain that value. If <varname>A</varname> is unset prior to the above, <varname>A</varname> will be set to <literal>someothervalue</literal>. This is a lazy version of ??=, in that the assignment does not occur until the end of the parsing process, so that the last, rather than the first, ??= assignment to a given variable will be used.</para>
95 </section> 101 </section>
96 <section> 102 <section>
97 <title>Immediate variable expansion (:=)</title> 103 <title>Immediate variable expansion (:=)</title>