StackOverflow2013

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copied!<p>Compiler-verified exceptions as part of a function's signature have two (theoretical) advantages: compiler optimizations and compile-time error checking.</p> <p>What is the difference, in terms of the compiler, between a function that throws exception class <code>X</code> and class <code>Y</code>? Ultimately... nothing at all. What kind of optimization could the compiler do with exception class <code>X</code> that it couldn't do with <code>Y</code>? Unless <code>std::exception</code> were special (and <code>X</code> were derived from it, while <code>Y</code> was not), what would it matter to the compiler?</p> <p>Ultimately, the only thing a compiler would care about in terms of optimization is whether a function will throw <em>any</em> exceptions or not. That's why the standards committee for C++11 ditched <code>throw(...)</code> in favor of <code>noexcept</code>, which states that the function will throw nothing.</p> <p>As for compile-time error checking, Java clearly shows how well this works. You're writing a function, <code>foo</code>. Your design has that it throws <code>X</code> and <code>Y</code>. Other pieces of code use <code>foo</code>, and they throw whatever <code>foo</code> throws. But the exception specification doesn't say "whatever <code>foo</code> throws". It must list <code>X</code> and <code>Y</code> specifically.</p> <p>Now you go back and change <code>foo</code> so that it no longer throws <code>X</code>, but now it throws <code>Z</code>. Suddenly, the entire project stops compiling. You must now go to every function that throws whatever <code>foo</code> threw just to change its exception specification to match <code>foo</code>.</p> <p>Eventually, a programmer just throws up their hand and says that it throws any exception. When you abandon a feature like that, it's a de facto admission that the feature is doing more harm than good.</p> <p>It's not that they <em>cannot</em> be useful. It's just that actual use of them shows that they're generally not useful. So there's no point.</p> <p>Plus, remember that C++'s specification states that no specification means that anything will be thrown, not nothing (as in Java). The simplest way to use the language is exactly that way: no checking. So there are going to be plenty of people who don't want the bother of using it.</p> <p>What good is a feature that many don't want to bother with, and even those who do will generally get a lot of grief out of it?</p>

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