With respect to "compile time optimisation in Ada" , the Ada language doesn't say anything about this. All it would say here is that the program must behave as if the function were called twice, i.e. it must produce the same results. But if the compiler "knows" that the function would produce the exact same result the second time, it can generate code that calls it only once. It can't do this for a function call in general, because a function could include side effects or use global variables that whose values could have changed. In this case, since the effects of Ada.Strings.Fixed.Trim
are defined by the language and since those effects do guarantee that the effects would be the same, a compiler could, in theory, mark this function as one for which a call with the exact same parameters could be optimized. (A function in a Pure
package would definitely be one where a second call could be eliminated, but unfortunately Ada.Strings.Fixed
isn't defined by the Ada language as being Pure
.) To find out whether a compiler actually does this particular optimization, though, you'd have to try it and check the code. I believe that if Test_String
is not marked as Volatile
, then compilers are allowed to assume that its value will be the same for each Ada.Strings.Fixed.Trim
call (i.e. it can't be changed by another task in between the calls), but I'm not 100% sure about this.
I'd declare a constant to hold the result (like Simon), but for me this is more out of a desire to avoid duplicated code than it is out of a concern for efficiency.