Re: use exception in default catch(...)
Seungbeom Kim wrote:
Al wrote:
Seungbeom Kim wrote:
Al wrote:
try {
doSomething();
}
template <typename T>
catch(const T& e) {
cerr << "Exception: " << e << endl;
log<T>(e);
}
This is impossible. Exceptions are a run-time mechanism, while templates
are a compile-time mechanism, so they don't mix. How could the compiler
figure out what kind of exceptions would be thrown by doSomething() and
generate different catch blocks for different types?
Assuming all the source is available, the compiler has all the
information it needs to figure out which exception types can bubble to a
given try-catch block, I believe.
C and C++ have allowed separate compilation (and I think it's done in
most cases), but this feature would *require* having all the source code
available at the compile step.
Not necessarily, but it would require a lot more information
than is normally available in an object file. I think one of
the goals of C++ is that it be able to use the "standard" object
files for the platform on which it is running.
Also, what I illustrated is just an example. I used template-like syntax
because it is familiar, but any syntax really would be fine
(compile-time or runtime).
You cannot use the run-time type information for anything other than
polymorphic classes (i.e. with virtual functions).
That's the current rule. It's based on the premise that you
cannot obtain the information for an arbitrary variable, that
e.g. the compiler has no way of finding out what a void* is
really pointing to. The is a reasonable constraint in the
general case, since it would require some additional information
somewhere, and very definitly have considerable cost to all
programs, whether they used the feature or not.
For example, when
an int or a std::pair is thrown, there's no way to recover the type
information at run-time.
When an object is thrown, the compiler IS required to maintain
some sort of type information concerning it, in order to match
the catch clause. It's a special case. And I would imagine
that in most implementations, this information is somehow
integrated with the RTTI system; that it is possible (for the
compiler) to go between this information and a type_info.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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