From: Richard Kreckel <kreckel@ginac.de>
Date: Mon, 25 Nov 2024 23:21:28 +0000 (+0100)
Subject: Avoid "expression with side effects..." warning using ex_to<T>().
X-Git-Tag: release_1-8-8~8
X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?a=commitdiff_plain;h=32702f847fb49da649f4362b0de3084890ac8129;p=ginac.git

Avoid "expression with side effects..." warning using ex_to<T>().

Clang++ warns that instantiations of this inline template function
ex_to<T>(const ex &) are "expression with side effects [that] will be
evaluated despite being used as an operand to 'typeid'".

Let's declare this ex_to<T>() as a pure function (i.e. having no
side effects) for compilers which support __attribute__((__pure__)).

GCC seems to support this attribute since more than ten years.
---

diff --git a/ginac/compiler.h b/ginac/compiler.h
index e9682794..0216b681 100644
--- a/ginac/compiler.h
+++ b/ginac/compiler.h
@@ -27,10 +27,12 @@
 #define unlikely(cond) __builtin_expect((cond), 0)
 #define likely(cond) __builtin_expect((cond), 1)
 #define attribute_deprecated __attribute__ ((deprecated))
+#define attribute_pure __attribute__((__pure__))
 #else
 #define unlikely(cond) (cond)
 #define likely(cond) (cond)
 #define attribute_deprecated
+#define attribute_pure
 #endif
 
 #endif // ndef GINAC_COMPILER_DEP_H
diff --git a/ginac/ex.h b/ginac/ex.h
index 5381a38a..37d74e7b 100644
--- a/ginac/ex.h
+++ b/ginac/ex.h
@@ -25,6 +25,7 @@
 
 #include "basic.h"
 #include "ptr.h"
+#include "compiler.h"
 
 #include <functional>
 #include <iosfwd>
@@ -973,7 +974,7 @@ inline bool is_exactly_a(const ex &obj)
  *  @param e expression
  *  @return reference to object of class T
  *  @see is_exactly_a<class T>() */
-template <class T>
+template <class T> attribute_pure
 inline const T &ex_to(const ex &e)
 {
 	GINAC_ASSERT(is_a<T>(e));