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authorBjörn Gustavsson <[email protected]>2018-05-17 14:10:58 +0200
committerGitHub <[email protected]>2018-05-17 14:10:58 +0200
commit52fe21127a1e2d82a0239e8e46467ad9b778677f (patch)
tree63e426f664f996774ac40a9273235b20674063b4 /system/doc
parentb65538a9598981764b018e1cda409a36957a6ee7 (diff)
parent46237d41e7455ae5801d78e85a82216b73697f44 (diff)
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Merge pull request #1810 from tomas-abrahamsson/bjorn/preprocessor-extensions
Add ?OTP_RELEASE, -if and -elif to the preprocessor OTP-15087
Diffstat (limited to 'system/doc')
-rw-r--r--system/doc/reference_manual/macros.xml35
1 files changed, 33 insertions, 2 deletions
diff --git a/system/doc/reference_manual/macros.xml b/system/doc/reference_manual/macros.xml
index a341307ab7..760599308c 100644
--- a/system/doc/reference_manual/macros.xml
+++ b/system/doc/reference_manual/macros.xml
@@ -150,6 +150,11 @@ bar(X) ->
<item>The name of the current function.</item>
<tag><c>?FUNCTION_ARITY</c></tag>
<item>The arity (number of arguments) for the current function.</item>
+ <tag><c>?OTP_RELEASE</c></tag>
+ <item>The OTP release that the currently executing ERTS
+ application is part of, as an integer. For details, see
+ <seealso marker="erts:erlang#system_info/1"><c>erlang:system_info(otp_release)</c></seealso>.
+ This macro was introduced in OTP release 21.</item>
</taglist>
</section>
@@ -202,8 +207,16 @@ f() ->
directive. If that condition is false, the lines following
<c>else</c> are evaluated instead.</item>
<tag><c>-endif.</c></tag>
- <item>Specifies the end of an <c>ifdef</c> or <c>ifndef</c>
- directive.</item>
+ <item>Specifies the end of an <c>ifdef</c>, an <c>ifndef</c>
+ directive, or the end of an <c>if</c> or <c>elif</c> directive.</item>
+ <tag><c>-if(Condition).</c></tag>
+ <item>Evaluates the following lines only if <c>Condition</c>
+ evaluates to true.</item>
+ <tag><c>-elif(Condition).</c></tag>
+ <item>Only allowed after an <c>if</c> or another <c>elif</c> directive.
+ If the preceding <c>if</c> or <c>elif</c> directives do not
+ evaluate to true, and the <c>Condition</c> evaluates to true,
+ the lines following the <c>elif</c> are evaluated instead.</item>
</taglist>
<note>
<p>The macro directives cannot be used inside functions.</p>
@@ -231,6 +244,24 @@ or
{ok,m}</pre>
<p><c>?LOG(Arg)</c> is then expanded to a call to <c>io:format/2</c>
and provide the user with some simple trace output.</p>
+
+ <p><em>Example:</em></p>
+ <code type="none">
+-module(m)
+...
+-ifdef(OTP_RELEASE).
+ %% OTP 21 or higher
+ -if(?OTP_RELEASE >= 22).
+ %% Code that will work in OTP 22 or higher
+ -elif(?OTP_RELEASE >= 21).
+ %% Code that will work in OTP 21 or higher
+ -endif.
+-else.
+ %% OTP 20 or lower.
+-endif.
+...</code>
+ <p>The code uses the <c>OTP_RELEASE</c> macro to conditionally
+ select code depending on release.</p>
</section>
<section>