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    <p>This is one of cases much more tricky than one can initially expect.</p> <p>One of important and useful features D has over C++ is that every single type (including all user types) has some initial non-garbage value that can be evaluated at compile-time. It is used as <code>T.init</code> and has two important use cases:</p> <ol> <li><p>Template constraints can use T.init value to check if certain operations can be done on given type (quoting Kenji Hara's snippet):</p> <pre><code>template isSomething(T) { enum isSomething = is(typeof({ //T t1; // not good if T is nested struct, or has @disable this() //T t2 = void; auto x = t2; // not good if T is non-mutable type T t = T.init; // avoid default construct check ...use t... })); } </code></pre></li> <li><p>Your variables are always initialized properly unless you explicitly use <code>int i = void</code> syntax. No garbage possible.</p></li> </ol> <p>Given that, difficult question arises. Should we guarantee that T() and T.init are the same (as many programmers coming from C++ will expect) or allow default construction that may easily destroy that guarantee. As far as I know, decision was made that first approach is safer, despite being surprising.</p> <p>However, discussions keep popping with various improvements proposed (for example, allowing CTFE-able default constructor). One <a href="http://forum.dlang.org/post/mailman.1362.1368826464.4724.digitalmars-d@puremagic.com" rel="noreferrer">such thread</a> has appeared very recently.</p>
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