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Help: Clarify behavior of if(DEFINED) for cache and non-cache variables

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Fixes: #23023
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Craig Scott
2021-12-20 19:27:39 +11:00
parent 6b5c836252
commit a45e922768
1 changed files with 10 additions and 1 deletions
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11
Help/command/if.rst
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@@ -126,7 +126,16 @@ Existence Checks
``if(DEFINED <name>|CACHE{<name>}|ENV{<name>})``
True if a variable, cache variable or environment variable
with given ``<name>`` is defined. The value of the variable
does not matter. Note that macro arguments are not variables.
does not matter. Note the following caveats:
* Macro arguments are not variables.
* It is not possible to test directly whether a `<name>` is a non-cache
variable. The expression ``if(DEFINED someName)`` will evaluate to true
if either a cache or non-cache variable ``someName`` exists. In
comparison, the expression ``if(DEFINED CACHE{someName})`` will only
evaluate to true if a cache variable ``someName`` exists. Both expressions
need to be tested if you need to know whether a non-cache variable exists:
``if(DEFINED someName AND NOT DEFINED CACHE{someName})``.
.. versionadded:: 3.14
Added support for ``CACHE{<name>}`` variables.