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POIs this the best way to do a "with" statement in C++?
 

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  1. POIs this the best way to do a "with" statement in C++?
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    <p><strong>Edit:</strong></p> <p>So this question was misinterpreted to such a ludicrous degree that it has no point anymore. I don't know <em>how</em>, since the question that I actually <em>asked</em> was whether <em>my specific implementation</em> of this&mdash;yes, known to be pointless, yes, not remotely resembling idiomatic C++&mdash;macro was as good as it could be, and whether it necessarily had to use <code>auto</code>, or if there was a suitable workaround instead. It was not supposed to generate this much attention, and certainly not a misunderstanding of this magnitude. It's pointless to ask respondents to edit their answers, I don't want anybody to lose reputation over this, and there's some good information floating around in here for potential future viewers, so I'm going to arbitrarily pick one of the lower-voted answers to evenly distribute the reputation involved. Move along, nothing to see here.</p> <hr> <p>I saw <a href="https://stackoverflow.com/questions/601153/missing-the-with-keyword-in-c">this question</a> and decided it might be fun to write a <code>with</code> statement in C++. The <code>auto</code> keyword makes this really easy, but is there a better way to do it, perhaps without using <code>auto</code>? I've elided certain bits of the code for brevity.</p> <pre><code>template&lt;class T&gt; struct with_helper { with_helper(T&amp; v) : value(v), alive(true) {} T* operator-&gt;() { return &amp;value; } T&amp; operator*() { return value; } T&amp; value; bool alive; }; template&lt;class T&gt; struct with_helper&lt;const T&gt; { ... }; template&lt;class T&gt; with_helper&lt;T&gt; make_with_helper(T&amp; value) { ... } template&lt;class T&gt; with_helper&lt;const T&gt; make_with_helper(const T&amp; value) { ... } #define with(value) \ for (auto o = make_with_helper(value); o.alive; o.alive = false) </code></pre> <p>Here's an (updated) usage example with a more typical case that shows the use of <code>with</code> as it is found in other languages.</p> <pre><code>int main(int argc, char** argv) { Object object; with (object) { o-&gt;member = 0; o-&gt;method(1); o-&gt;method(2); o-&gt;method(3); } with (object.get_property("foo").perform_task(1, 2, 3).result()) { std::cout &lt;&lt; (*o)[0] &lt;&lt; '\n' &lt;&lt; (*o)[1] &lt;&lt; '\n' &lt;&lt; (*o)[2] &lt;&lt; '\n'; } return 0; } </code></pre> <p>I chose <code>o</code> because it's an uncommon identifier, and its form gives the impression of a "generic thing". If you've got an idea for a better identifier or a more usable syntax altogether, then please do suggest it.</p>
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    1. USJon Purdy
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    1. COThanks...Looks interesting and useful.
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    2. CO@Robert Harvey: It's basically just shorthand for `{ [const] auto& o = ...; ... }`, but slightly less ugly.
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    3. CODo you mean `#define with(value) \ ` instead of `#define with(value, id) \ `? BTW, how about Boost.Typeof?
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