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POHow to handle 'this' pointer in constructor?
 

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  1. POHow to handle 'this' pointer in constructor?
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    <p>I have objects which create other child objects within their constructors, passing 'this' so the child can save a pointer back to its parent. I use boost::shared_ptr extensively in my programming as a safer alternative to std::auto_ptr or raw pointers. So the child would have code such as <code>shared_ptr&lt;Parent&gt;</code>, and boost provides the <a href="http://boost.org/doc/libs/release/libs/smart_ptr/enable_shared_from_this.html" rel="noreferrer"><code>shared_from_this()</code></a> method which the parent can give to the child.</p> <p>My problem is that <code>shared_from_this()</code> cannot be used in a constructor, which isn't really a crime because 'this' should not be used in a constructor anyways unless you know what you're doing and don't mind the limitations.</p> <p>Google's C++ Style Guide <a href="http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Doing_Work_in_Constructors#Doing_Work_in_Constructors" rel="noreferrer">states</a> that constructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. This solves the 'this-in-constructor' problem as well as a few others as well.</p> <p>What bothers me is that people using your code now must remember to call Init() every time they construct one of your objects. The only way I can think of to enforce this is by having an assertion that Init() has already been called at the top of every member function, but this is tedious to write and cumbersome to execute. </p> <p>Are there any idioms out there that solve this problem at any step along the way?</p>
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    1. COGoogle is wrong. There's a giant thread on this and other short-comings of their style guide on comp.lang.c++.moderated. The basic reason for them coming up with this is because they also (wrongly) ban exceptions.
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    2. CO@Neil: The impression I got was that Google was being heavy-handed with the style guide to accomodate people who don't know C++ well, trying to limit the damage they could do, or perhaps to enforce uniformity with legacy code. Google may have good reasons for their style guide, but it's not a good model for anybody else to copy.
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      1. USDavid Thornley
    3. CO@David That's correct. But people can get confused using floating point numbers (look at all the questions here on the topic) or even integers, but we don't ban their use. This is one of the reasons I am no fan of style guides.
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