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-rw-r--r-- | bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml index b3e7dd8d9e..862a6bddfe 100644 --- a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml +++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml @@ -652,6 +652,51 @@ after the "inherit" statement. </note> </para> + + <para> + If necessary, it is possible to inherit a class + conditionally by using + a variable expression after the <filename>inherit</filename> + statement. + Here is an example: + <literallayout class='monospaced'> + inherit ${VARNAME} + </literallayout> + If <filename>VARNAME</filename> is going to be set, it needs + to be set before the <filename>inherit</filename> statement + is parsed. + One way to achieve a conditional inherit in this case is to use + overrides: + <literallayout class='monospaced'> + VARIABLE = "" + VARIABLE_someoverride = "myclass" + </literallayout> + </para> + + <para> + Another method is by using anonymous Python. + Here is an example: + <literallayout class='monospaced'> + python () { + if condition == value: + d.setVar('VARIABLE', 'myclass') + else: + d.setVar('VARIABLE', '') + } + </literallayout> + </para> + + <para> + Alternatively, you could use an in-line Python expression + in the following form: + <literallayout class='monospaced'> + inherit ${@'classname' if condition else ''} + inherit ${@functionname(params)} + </literallayout> + In all cases, if the expression evaluates to an empty + string, the statement does not trigger a syntax error + because it becomes a no-op. + </para> </section> <section id='include-directive'> |