missing #ifndef

new functions ifelse

mrw/stdext.hpp

@@ -9,6 +9,10 @@
     @license LGPL, see file <a href="license.html">COPYING</a>
 
     $Log$
+    Revision 1.6  2005/02/18 15:47:23  marc
+    missing #ifndef
+    new functions ifelse
+
     Revision 1.5  2005/01/28 07:52:33  marc
     typo in doc
 
@@ -27,6 +31,9 @@
 
 */
 
+#ifndef __MRW__STDEXT_HPP__
+#define __MRW__STDEXT_HPP__
+
 #include <string>
 #include <iostream>
 #include <algorithm>
@@ -37,7 +44,13 @@ namespace mrw {
    */
   //@{
 
-  /** @defgroup stdextReadline Read Line
+  /** @defgroup stdextFunction Useful Global Functions
+
+       - @ref getline read exactly one line from a stream
+       - @ref ifelse implements a dual <code>?:</code> operator, like:
+              <code>a&nbsp;?&nbsp;a&nbsp;:&nbsp;b</code>      
+
+      @section stdextReadline Read Line
       
       The global functions mrw::getline read exactly one line from a
       stream, without the need of a buffer. It is therefore guaranteed
@@ -94,6 +107,36 @@ namespace mrw {
     return std::max(a, b);
   }
 
+  /** @brief Dual <code>?:</code> operation:
+             <code>a&nbsp;?&nbsp;a&nbsp;:&nbsp;b</code>
+
+      If the first parameter is not @c 0, then it is returned,
+      otherwise the second parameter is returned. It is equivalent to
+      the construct: <code>a&nbsp;?&nbsp;a&nbsp;:&nbsp;b</code>, but without
+      the side effect of duplicated evaluation of parameter
+      <code>a</code>.
+
+      Older gcc compiler implemented the non standard extension of
+      <code>a?:b</code>, which was exactly the same.
+
+      @param a criteria that is checked and returned if not @c 0
+      @param b alternative value to be returned if @c a is @c 0
+      @return <code>a&nbsp;?&nbsp;a&nbsp;:&nbsp;b</code>
+      @pre #include <mrw/stdext.hpp>
+      @pre @c T must be convertible to @c bool
+  */
+  template<typename T> const T& ifelse(const T& a, const T& b) {
+    return a?a:b;
+  }
+
+  /** @brief Dual <code>?:</code> operation:
+             <code>a&nbsp;?&nbsp;a&nbsp;:&nbsp;b</code>
+
+      @copydoc ifelse(const T& a, const T& b) */
+  template<typename T> const T* ifelse(const T* a, const T* b) {
+    return a?a:b;
+  }
+
   /** @brief read one line from a stream
 
       Reads one line from a stream, up to delimiter @c d.
@@ -123,3 +166,5 @@ namespace mrw {
   //@}
   //@}
 }
+
+#endif