I use something similar in a container library to warn the user if he or she supplies an argument with potential side effects to a macro that evaluates it multi

I use something similar in a container library to warn the user if he or she supplies an argument with potential side effects to a macro that evaluates it multiple times: https://github.com/JacksonAllan/CC/blob/42a7d810274a698dff87a6cdbecd91e93798afad/cc.h#L1284 https://github.com/JacksonAllan/CC/blob/42a7d810274a698dff87... Specifically, if (arg)==(arg) is not a constant expression, then it could have side effects. However, this mechanism does generate some annoying false positives, as shown below: // Create a map with int keys and values that are vectors of floats: map( int, vec( float ) ) our_map; init( &our_map ); // Create a vector of floats: vec( float ) our_vec; init( &our_vec ); push( &our_vec, 1.23f ); // Insert the vector into the map. insert( &our_map, 456, our_vec ); // Generates a warning because get checks its first argument for side // effects and the compiler can't tell that the first argument of the // outermost get has none: printf( "%f", *get( get( &our_map, 456 ), 0 ) ); // The "proper", albeit cumbersome, way to achieve the same thing without a // warning: vec( float ) *itr = get( &our_map, 456 ); printf( "%f", *get( itr, 0 ) );