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    <p>There is no MRO in C++ like Python. If a method is ambiguous, it is a compile-time error. Whether a method is virtual or not doesn't affect it, but virtual <em>inheritance</em> will.</p> <hr> <p>The algorithm is described in the C++ standard &sect;[class.member.lookup] (10.2). Basically it will find the closest unambiguous implementation in the superclass graph. The algorithm works like this:</p> <ol> <li><p>Suppose you want to look up a function <strong>f</strong> in class <strong>C</strong>.</p></li> <li><p>We define a <em>look-up set</em> <strong>S(f, C)</strong> being a pair of sets (<strong>&Delta;</strong>, <strong>&Sigma;</strong>) representing all possibilities. <sub>(&sect;10.2/3)</sub></p> <ul> <li><p>The set <strong>&Delta;</strong> is called the <em>declaration set</em>, which is basically all the possible <strong>f</strong>'s.</p></li> <li><p>The set <strong>&Sigma;</strong> is called the <em>subobject set</em>, which contain the classes that these <strong>f</strong>'s are found.</p></li> </ul></li> <li><p>Let <strong>S(f, C)</strong> include all <strong>f</strong> directly defined (or <code>using</code>-ed) in <strong>C</strong>, if any <sub>(&sect;10.2/4)</sub>:</p> <pre><code>Δ = {f in C}; if (Δ != empty) Σ = {C}; else Σ = empty; S(f, C) = (Δ, Σ); </code></pre></li> <li><p>If <strong>S(f, C)</strong> is empty <sub>(&sect;10.2/5)</sub>, </p> <ul> <li><p>Compute <strong>S(f, B<sub>i</sub>)</strong> where <strong>B<sub>i</sub></strong> is a base class of <strong>C</strong>, for all <em>i</em>.</p></li> <li><p>Merge each <strong>S(f, B<sub>i</sub>)</strong> into <strong>S(f, C)</strong> one by one.</p> <pre><code>if (S(f, C) == (empty, empty)) { B = base classes of C; for (Bi in B) S(f, C) = S(f, C) .Merge. S(f, Bi); } </code></pre></li> </ul></li> <li><p>Finally the declaration set is returned as the result of name resolution <sub>(&sect;10.2/7)</sub>.</p> <pre><code>return S(f, C).Δ; </code></pre></li> <li><p>The merge between two look-up sets (<strong>&Delta;<sub>1</sub></strong>, <strong>&Sigma;<sub>1</sub></strong>) and (<strong>&Delta;<sub>2</sub></strong>, <strong>&Sigma;<sub>2</sub></strong>) is defined as <sub>(&sect;10.2/6)</sub>:</p> <ul> <li>If every class in <strong>Σ<sub>1</sub></strong> is a base class of at least one class in <strong>Σ<sub>2</sub></strong>, return (<strong>&Delta;<sub>2</sub></strong>, <strong>Σ<sub>2</sub></strong>).<br> (Similar for the reverse.)</li> <li>Else if <strong>Δ<sub>1</sub></strong> ≠ <strong>Δ<sub>2</sub></strong>, return (<em>ambiguous</em>, <strong>Σ<sub>1</sub></strong> &cup; <strong>Σ<sub>2</sub></strong>).</li> <li><p>Otherwise, return (<strong>Δ<sub>1</sub></strong>, <strong>Σ<sub>1</sub></strong> &cup; <strong>Σ<sub>2</sub></strong>)</p> <pre><code>function Merge ( (Δ1, Σ1), (Δ2, Σ2) ) { function IsBaseOf(Σp, Σq) { for (B1 in Σp) { if (not any(B1 is base of C for (C in Σq))) return false; } return true; } if (Σ1 .IsBaseOf. Σ2) return (Δ2, Σ2); else if (Σ2 .IsBaseOf. Σ1) return (Δ1, Σ1); else { Σ = Σ1 union Σ2; if (Δ1 != Δ2) Δ = ambiguous; else Δ = Δ1; return (Δ, Σ); } } </code></pre></li> </ul></li> </ol> <hr> <p>For example <sub>(&sect;10.2/10)</sub>,</p> <pre><code>struct V { int f(); }; struct W { int g(); }; struct B : W, virtual V { int f(); int g(); }; struct C : W, virtual V { }; struct D : B, C { void glorp () { f(); g(); } }; </code></pre> <p>We compute that</p> <pre><code>S(f, D) = S(f, B from D) .Merge. S(f, C from D) = ({B::f}, {B from D}) .Merge. S(f, W from C from D) .Merge. S(f, V) = ({B::f}, {B from D}) .Merge. empty .Merge. ({V::f}, {V}) = ({B::f}, {B from D}) // fine, V is a base class of B. </code></pre> <p>and</p> <pre><code>S(g, D) = S(g, B from D) .Merge. S(g, C from D) = ({B::g}, {B from D}) .Merge. S(g, W from C from D) .Merge. S(g, V) = ({B::g}, {B from D}) .Merge. ({W::g}, {W from C from D}) .Merge. empty = (ambiguous, {B from D, W from C from D}) // the W from C is unrelated to B. </code></pre>
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    1. COhttp://www.csci.csusb.edu/dick/c++std/cd2/derived.html#class.member.lookup
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    2. COThanks for the detailed description :) That's exactly what I needed.
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