simplified case:<div><br></div><div>doesn't work with NRVO:<br><div>
<font face="Menlo">
<span style="color:#009695">void</span><span style="color:#444444"> </span><span style="color:#444444">main</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#009695">immutable</span><span style="color:#444444"> </span><span style="color:#009695">int</span><span style="color:#444444">[</span><span style="color:#f57d00">10</span><span style="color:#444444">]</span><span style="color:#444444"> </span><span style="color:#444444">x</span><span style="color:#444444"> </span><span style="color:#444444">=</span><span style="color:#444444"> </span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444"> </span><span style="color:#009695">pure</span><span style="color:#444444"> </span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#009695">int</span><span style="color:#444444">[</span><span style="color:#f57d00">10</span><span style="color:#444444">]</span><span style="color:#444444"> </span><span style="color:#444444">x_</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#009695">debug</span><span style="color:#444444"> </span><span style="color:#444444">printf</span><span style="color:#444444">(</span><span style="color:#f57d00">"</span><span style="color:#f57d00">&x_[0] = %p</span><span style="color:#a53e00">\n</span><span style="color:#f57d00">"</span><span style="color:#444444">,</span><span style="color:#444444"> </span><span style="color:#444444">&</span><span style="color:#444444">x_</span><span style="color:#444444">[</span><span style="color:#f57d00">0</span><span style="color:#444444">]</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#009695">return</span><span style="color:#444444"> </span><span style="color:#444444">x_</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444">}</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#009695">debug</span><span style="color:#444444"> </span><span style="color:#444444">printf</span><span style="color:#444444">(</span><span style="color:#f57d00">"</span><span style="color:#f57d00">&x[0] = %p</span><span style="color:#a53e00">\n</span><span style="color:#f57d00">"</span><span style="color:#444444">,</span><span style="color:#444444"> </span><span style="color:#444444">&</span><span style="color:#444444">x</span><span style="color:#444444">[</span><span style="color:#f57d00">0</span><span style="color:#444444">]</span><span style="color:#444444">)</span><span style="color:#444444">;</span><span style="color:#444444"> </span><span style="color:#444444"> // prints different address</span><br>
<span style="color:#444444">}</span></font> </div><div><br></div><div><br></div><div>doesn't work with RVO:</div><div>
<font face="Menlo">
<span style="color:#009695">struct</span><span style="color:#444444"> </span><span style="color:#444444">A</span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#009695">int</span><span style="color:#444444">[</span><span style="color:#f57d00">10</span><span style="color:#444444">]</span><span style="color:#444444"> </span><span style="color:#444444">x_</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#009695">this</span><span style="color:#444444">(</span><span style="color:#009695">int</span><span style="color:#444444"> </span><span style="color:#444444">_ignore</span><span style="color:#444444">)</span><span style="color:#009695">pure</span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#444444">foo</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444">}</span><br>
<span style="color:#444444"> </span><span style="color:#009695">void</span><span style="color:#444444"> </span><span style="color:#444444">foo</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#009695">const</span><span style="color:#444444"> </span><span style="color:#009695">pure</span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#009695">debug</span><span style="color:#444444"> </span><span style="color:#444444">printf</span><span style="color:#444444">(</span><span style="color:#f57d00">"</span><span style="color:#f57d00">&x_[0] = %p</span><span style="color:#a53e00">\n</span><span style="color:#f57d00">"</span><span style="color:#444444">,</span><span style="color:#444444"> </span><span style="color:#444444">&</span><span style="color:#444444">x_</span><span style="color:#444444">[</span><span style="color:#f57d00">0</span><span style="color:#444444">]</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444">}</span><br>
<span style="color:#444444">}</span><br>
<span style="color:#009695">void</span><span style="color:#444444"> </span><span style="color:#444444">main</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#009695">immutable</span><span style="color:#444444"> </span><span style="color:#444444">A</span><span style="color:#444444"> </span><span style="color:#444444">a</span><span style="color:#444444"> </span><span style="color:#444444">=</span><span style="color:#444444"> </span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444"> </span><span style="color:#009695">pure</span><span style="color:#444444"> </span><span style="color:#444444">{</span><br>
<span style="color:#444444"> </span><span style="color:#444444"> </span><span style="color:#009695">return</span><span style="color:#444444"> </span><span style="color:#444444">A</span><span style="color:#444444">(</span><span style="color:#f57d00">0</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444">}</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444"> </span><span style="color:#444444">a</span><span style="color:#444444">.</span><span style="color:#444444">foo</span><span style="color:#444444">(</span><span style="color:#444444">)</span><span style="color:#444444">;</span><br>
<span style="color:#444444">}</span><br>
</font></div><div> </div><div><br></div><div>is RVO even happening?</div><div><br><div class="gmail_quote">On Thu, May 16, 2013 at 1:55 AM, Kenji Hara <span dir="ltr"><<a href="mailto:k.hara.pg@gmail.com" target="_blank">k.hara.pg@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div class="h5"><div class="gmail_extra"><div class="gmail_quote">2013/5/16 TommiT <span dir="ltr"><<a href="mailto:tommitissari@hotmail.com" target="_blank">tommitissari@hotmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
I'd like to make it easier to initialize function local immutable/const data. Here's the type of problem I'd like to alleviate:<br>
<br>
const string[100] int__str;<br>
const int[string] str__int;<br>
<br>
for (int i = 0; i < 100; ++i)<br>
{<br>
auto str = to!string(i);<br>
int__str[i] = str; // ERROR: Can't modify const<br>
str__int[str] = i; // ERROR: Can't modify const<br>
}<br>
<br>
In short, I want to initialize two different const variables at once (in the same loop or other block). If I needed to initialize only one const variable, I could use a lambda:<br>
<br>
const string[100] int__str = {<br>
string[100] tmp;<br>
// ... init tmp ...<br>
return tmp;<br>
}();<br>
<br>
...But I can't see any easy solution for initializing two or more const variables at the same time.<br>
<br>
Here's my proposal: "initialization scope". You'd use it like this:<br>
<br>
initialization {<br>
const string[100] int__str;<br>
const int[string] str__int;<br>
<br>
for (int i = 0; i < 100; ++i)<br>
{<br>
auto str = to!string(i);<br>
int__str[i] = str; // OK<br>
str__int[str] = i; // OK<br>
}<br>
}<br>
<br>
string s = int__str[42]; // OK<br>
int__str[42] = "43" // ERROR: Can't modify const<br>
<br>
As you can see, 'initialization scope' would be a scope that is not a lexical scope (like static if), it merely makes all const and immutable variables created in that scope modifiable inside that scope but not after it.<br>
</blockquote></div><br></div></div></div><div class="gmail_extra">Pure delegate and implicit conversion for unique expression should work.</div><div class="gmail_extra"><br></div><div class="gmail_extra">import std.conv;</div>
<div class="gmail_extra">
<div class="gmail_extra">void main()</div><div class="gmail_extra">{</div><div class="gmail_extra"> immutable string[100] int__str = () pure {</div><div class="gmail_extra"> string[100] tmp;</div><div class="gmail_extra">
debug printf("&tmp[0] = %p\n", &tmp[0]); // [1]</div><div class="im"><div class="gmail_extra"> for (int i = 0; i < 100; ++i)</div><div class="gmail_extra"> {</div><div class="gmail_extra">
auto str = to!string(i);</div></div><div class="gmail_extra"> // BUG: pure function '__lambda1' cannot call impure function 'to'</div><div class="gmail_extra"> tmp[i] = str;</div>
<div class="gmail_extra"> }</div><div class="gmail_extra"> return tmp; // BUG: NRVO doesn't work</div><div class="gmail_extra"> }();</div><div class="gmail_extra"> debug printf("&int__str[0] = %p\n", &int__str[0]); // [2]</div>
<div class="gmail_extra">}</div><div class="gmail_extra"><br></div><div class="gmail_extra">Compiler bug: Currently [1] and [2] does not print same address.</div><div class="gmail_extra">Phobos bug: Currently <a href="http://std.conv.to" target="_blank">std.conv.to</a> is not pure.</div>
<span class="HOEnZb"><font color="#888888">
<div><br></div><div>Kenji Hara</div></font></span></div></div>
</blockquote></div><br></div></div>