Andy Little wrote:
"Deane Yang" <deane_yang@yahoo.com> wrote in message news:ecpndi$2mb$1@sea.gmane.org...
Andy Little wrote:
Can the dimension checking part of the library be used without the SI unit system? For most other unit systems I use, I mainly need dimension checking and not conversions between different units, such as km or m? Thus just a quantity with dimensions would be useful to catch programming errors. Yes. In the signature fixed_quantity<Unit, ValueType>, the Unit parameter can be so modelled that it only allows base units to be used, and in this case there is no conversion overhead BTW, a multiply is simply a multiply of the numeric values for example). By default Quan wont work across Unit models (IOW the class template names of units must match), which means that attempting to do calculations between Units with different class template names will fail at compile time. By this means you can guarantee that you can prevent any conversions. (FWIW there is also the option to allow unit conversions but make them explicit, prompted by Deane Yang easrlier in this thread.)
I guess I wasn't particularly clear earlier in this thread, because fixed_quantity appears to be what I want. I'm sorry for not RTFM (I did try to read the documentation once, but my memory is not what it used to be), but I have two quick questions:
1) Does operator*(fixed_quantity<Unit1, ValueType1> x, fixed_quantity<Unit2, ValueType2> y) work and, if so, what is the result type, assuming that operator*(ValueType1 v, ValueType2 w) returns a ValueType3?
OK. The following relates to the CVS version currently on the two_param-branch, but much applies to previous versions of Quan/PQS.
Dealing with the ValueTypes first, the result type of ValueType1 * ValueType2 is encoded in the compile time expression: binary_operation<ValueType1,times, ValueType2>::type. The implementation provides a specialisation for inbuilt types, and this follows the promotion/conversion rules on the respective calc in the C++ standard. We have also been recently testing with boost::numeric::interval and (with the appropriate specialisations) this seems to be working now and I believe that other numeric UDT ValueTypes will now work OK.
Does this mean that if ValueType1, ValueType2, and ValueType3 are UDT's and I do something like: template <> struct binary_operation<ValueType1,ValueType2> { typedef ValueType3 type; }; then everything will work properly?
The dimension of the result is found by adding the respective dimensions of the operands. ... <snip>
Oops. I guess fixed_quantity has to have one of the physical dimensions represented in SI units, eh? Never mind.