Editing Unified Exception Class - Program Options Suggestion

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== Unified exception class ==

Back to [[Suggestions - program_options library]]

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program_option's exceptions should be grouped under one struct.  Currently, we have, e.g.:

<pre>
    class validation_error : public error { ... };
</pre>

Instead, it should be

<pre>
    class program_options_exception : public error { ... };
    class validation_error : public program_options_exception { ... };
</pre>

Then, for example, you could have:

<pre>
    try {
        ...
    } catch (exception& e) {
        if (dynamic_cast<program_options_exception*>(&e))
            cout << "Usage: " << ...;
    }
</pre>

to print a usage message only in the case of a program_options-generated exception.

- [[People/Chuck Messenger]]

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Actually, "error" is "boost::progam_options::error" --- i.e. it's the class from which all
program options exceptions are derived. Is that already what you propose?

- [[People/Vladimir Prus]]

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Oh -- so you've got your own "error"?  Yes, that satisfies what I wanted.

But, the symbol "error" doesn't seem wise.  I had assumed (probably
wrongly) that "error" was in the std namespace.  (Maybe I was thinking of "exception").  Even so, the word "error" is much too
common to be used in program_option's top level.

What happens when a user does "using namespace program_options;" (which is my typical way of using boost libs)?

You might counter that you can always specify program_options::error.  But I feel the genericness of the name is problematical.
What if a user doesn't qualify "error"?  Symbols in a library's toplevel
namespace should, I feel, be reasonably specific to the library's domain.

I suggest changing "error" to "program_options_error".

- [[People/Chuck Messenger]]

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I somehow don't like boost::program_options::program_options_error. I'm -0 on this proposal -- whatever
reviewers in general will decide, will do.

- [[People/Vladimir Prus]]

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Summary:
This change is a minor edit.
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