Re: [eigen] Eigen Types as Parameters for Functions |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Eigen Types as Parameters for Functions*From*: Márton Danóczy <marton78@xxxxxxxxx>*Date*: Wed, 27 Jun 2012 15:12:46 +0200*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; bh=YE8R45dOBWYu6KWs//1JXCrrNkzqkrmgzxkMyqz/ikw=; b=i9vOA/fCwx0GMCV2Tso2lNmiC6a+KuHpcej34C7WirPq/eLRUbemlHxqDmfAiqBQTx SgEoo5kBHXzBzLW7bSelfjfCg/wLAplAB+2salGMgEl1wBBrACIcBUMlha6OiTV3qZfn 0LlSF0+F3damCkmP33Qs7lipgcCFBZt8EY2+W9CG3ZGu+1LGQ3S6bbNTVcv34RIth37a DfUFJfyTJWDF0ZMyf4EJ64MXVRiJFlguu781ew4yyw1i651FAH6sqr9I9O6cjWPkgf9R bmu5+dF/C0BCmWAWT4QhcRFETfqs96wZFOLQPy/qFz0kxJt0ycIvMGhnWRFq7jSygCCc 4d9Q==

>> * Does A.row(3); change after calling foo1(A.row(3))? (i.e. is it >> copied back?) -- you could simply copy it back in the destructor, if >> match_helper<Derived>::type() is false_type. >> If you think back-copying causes too much performance penalty, you >> need to forbid this. >> Furthermore, it sometimes might be useful to mark Ref as a pure >> "out-ref" in this case, saving the copy from A.row() to m_object. > > That's a very good remark, and currently I don't have a strong opinion > whether we should copy-back or forbid it. The copy-back option is ok > when Ref is used for function arguments and in sequential algorithms, > but very dangerous in all other cases. For instance, I was thinking > about Ref<> inside Eigen itself to reduce template instantiations. In > this case you clearly don't want the copy-back approach. > On the other hand, I known it would be very convenient for many > users. Proposing both might be overkill. > What if Ref<Something> copies back while Ref<const Something> doesn't? Marton

**References**:**Re: [eigen] Eigen Types as Parameters for Functions***From:*Gael Guennebaud

**Re: [eigen] Eigen Types as Parameters for Functions***From:*Christoph Hertzberg

**Re: [eigen] Eigen Types as Parameters for Functions***From:*Gael Guennebaud

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