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    <p>As they are data fields that can be modified, they are not <code>const</code>.</p> <p>If you want to restrict post-construct access to them to <code>const</code>, you need to wrap them in accessors as follows:</p> <pre><code>struct ImageInfo { ImageInfo(const double &amp;ppix, /*...*/) : PpiX_(ppix), /*...*/ { } double const&amp; PpiX() const {return PpiX_; }; double const&amp; PpiY() const {return PipY_; }; int const&amp; SizeX() const {return SizeX_; }; int const&amp; SizeY() const {return SizeY_; }; private: double PpiX_; double PpiY_; int SizeX_; int SizeY_; }; </code></pre> <p>That allows move/copy assignment and construction, while blocking non-<code>const</code> access outside of said construction.</p> <p>Avoiding the <code>()</code> is tricky, but could be done with pseudo-references, something like this:</p> <pre><code>struct pseudo_const_reference_to_Ppix { ImageInfo const* self; operator double() const { return self-&gt;Ppix; } void reseat( ImageInfo const* o ) { self = o; } }; </code></pre> <p>plus a whole pile of boilerplate to overload every <code>const</code> operator on the left and right such that the above <code>pseudo_const_reference_*</code> is just as valid as <code>double</code>.</p> <p>Generic versions can be written (either taking a functor or a <code>std::function</code> if you are willing to suffer type erasure overhead).</p> <p>Then you maintain these pseudo-<code>const</code> references on assignment and copy/move construction.</p> <p>I think the <code>()</code> is the better option.</p> <p>Note that the overhead of a pointer (or more) per pseudo-reference is basically unavoidable: member variables do not have access to the <code>this</code> from which they are invoked, even though the accesing site has it right there plain as day.</p>
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    1. POHow do I assign a data object with const members?
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    1. USYakk - Adam Nevraumont
    1. USYakk - Adam Nevraumont
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    1. COYep, that's the first solution that came to my mind, too.
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      1. USMartin Hennings
    2. CO@Martin I have now included a sketch of a ridiculous solution that gets rid of the `()`.
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      1. USYakk - Adam Nevraumont
    3. COYou're right, that is ridiculous. :-)
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      1. USMartin Hennings
 

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