Re: [boost] [boost::throw_exception] and platforms where it don'tthrow

From: Thorsten Ottosen (tottosen_at_[hidden])
Date: 2005-12-09 16:39:43

Peter Dimov wrote:

 > Thorsten Ottosen wrote:
 >
 >
 >> Anyway, my feeling is that people that uses BOOST_NO_EXCEPTION would
 >> prefer
 >>
 >> if( foo() )
 >> BOOST_THROW_EXCEPTION( std::exception, "MSG" );
 >>
 >> where this expands to BOOST_ASSERT( "MSG" ) when BOOST_NO_EXCEPTION
 >> is true.
 >
 >
 >
 > This very much depends on foo(). In your case I suspect that foo() 
validates an input argument and the outer function is something similar 
to vector<>::at.
 >
 > Think about in which circumstances one would use at() - a function 
that "recovers gracefully" from input arguments out of range by throwing 
an exception - as opposed to operator[], a function that uses 
BOOST_ASSERT to check the input.
 >
 > Presumably, the client that calls at() _expects_ an exception when an 
out of range argument is passed, and this exception is handled 
somewhere; this indicates that out of range arguments to at() are 
expected and this code path forms an ordinary part of the program.
 >
 > If out of range input arguments were unexpected, one would use 
operator[], possibly guarded by a user-level assert.

I don't think it is that simple.

I've heard people saying they would like to use numeric_cast if it did 
not throw, but did an assertion.

 > To get back to throw_exception, I guess my point is that nothing is 
gained by turning the throw into an assert, because people that wanted 
an assert would use the asserting function, not the throwing function.

if that asserting function exists. it does not exists in many cases of 
the Pointer Container library.

I think there might also be people working on platforms with exceptions 
who would like to get rid of the exceptions to gain a little speed.

-Thorsten