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C++ UNO Coding Hints

Author: Daniel Bölzle

I want to show some common hints and peephole optimizations concerning C++ Any and Reference<> objects, although most of them have formerly been posted on interface-announce.

Here we go:

1. don't use:

        Any ret;
        ret <<= xFoo;
        return ret;
   

   for better performance use:

        return makeAny( xFoo );
   

   BTW: You can use makeAny() and <<=, >>= with every C++-UNO type and the C++ bool, except for sal_Unicode which conflicts with sal_uInt16, e.g.

        return makeAny( static_cast< sal_Int64 >(42) );
        return makeAny( Sequence< OUString >() );
        return makeAny( false );
   

   but

        sal_Unicode c = 'a';
        return Any( &c, ::getCppuCharType() );
   

2. don't use:

        Reference< XFoo > x;
        ...
        x = Reference< XFoo >( xSomething, UNO_QUERY );
   

   for better performance use:

        Reference< XFoo > x;
        ...
        x.set( xSomething, UNO_QUERY );
   

3. The following code:

        Any any;
        ...
        Reference< XFoo > x;
        any >>= x;
   

   can alternatively be written as:

        Any any;
        ...
        Reference< XFoo > x( any, UNO_QUERY );
   

   or

        Reference< XFoo > x;
        ...
        x.set( any, UNO_QUERY );
   

Additionally I recommend using UNO_QUERY_THROW (instead of UNO_QUERY). This will throw a ::com::sun::star::uno::RuntimeException with message

    "unsatisfied query for interface of type ...!"

     Reference< XFoo > xFoo( xBar, UNO_QUERY );
     if (! xFoo.is())
     {
         throw RuntimeException(..."got no XFoo!"...);
     }
     xFoo->foo();

     =>

     Reference< XFoo >( xBar, UNO_QUERY_THROW )->foo();