220 38916 article Path: news.gmane.org!.POSTED!not-for-mail From: Jake Arkinstall Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow forward class declarations to match a type alias. 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[209.85.220.41]) by mx.google.com with SMTPS id 68-v6sor3863302ion.18.2018.06.29.15.45.21 for (Google Transport Security); Fri, 29 Jun 2018 15:45:21 -0700 (PDT) Received-SPF: pass (google.com: domain of jake.arkinstall@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a6b:910a:: with SMTP id t10-v6mr14220200iod.59.1530312320623; Fri, 29 Jun 2018 15:45:20 -0700 (PDT) In-Reply-To: X-Original-Sender: jake.arkinstall@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=NjFzeNEC; spf=pass (google.com: domain of jake.arkinstall@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=jake.arkinstall@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:38916 Archived-At: --000000000000442a5e056fcf9a12 Content-Type: text/plain; charset="UTF-8" I had a similar refactoring once, and I approached it as follows. It might not apply, But as this does seem like an XY problem to me I thought it best to provide a potential solution. The real problem is that you have code that depends on a class that doesn't exist yet. Templates are your friend here. When you need to use FloatImage, provide it as a template parameter. You then get the upshot of being able to use your code with something other than a FloatImage in the future. You can also give CudaImage a "using value_type = T". That way any class which currently uses FloatImage can be given a template parameter T (which in your current code would be provided with FloatImage) can accept arguments of e.g. "typename T::value_type", and you aren't necessarily locked into using floats as arguments if someone comes along and wants a DoubleImage or something. If you want to restrict the types, concepts come to the rescue. If you have an API to preserve, rename the old classes and functions as necessary, and expose the FloatImage-specialised versions under the original names. If this doesn't sound like a convincing approach, the Eigen library is a beautiful example (I'm not sure whether it is the result of a refactor or of some brilliant foresight). -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAC%2B0CCMRC5JHx4N2JFzN960xfYsBVfKVt%3D7iSN5NCws3ALHkFA%40mail.gmail.com. --000000000000442a5e056fcf9a12 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
I had a = similar refactoring once, and I approached it as follows. It might not appl= y, But as this does seem like an XY problem to me I thought it best to prov= ide a potential solution.

= The real problem is that you have code that depends on a class that doesn&#= 39;t exist yet. Templates are your friend here. When you need to use FloatI= mage, provide it as a template parameter. You then get the upshot of being = able to use your code with something other than a FloatImage in the future.=

You can als= o give CudaImage a "using value_type =3D T". That way any class w= hich currently uses FloatImage can be given a template parameter T (which i= n your current code would be provided with FloatImage) can accept arguments= of e.g. "typename T::value_type", and you aren't necessarily= locked into using floats as arguments if someone comes along and wants a D= oubleImage or something. If you want to restrict the types, concepts come t= o the rescue.

If you hav= e an API to preserve, rename the old classes and functions as necessary, an= d expose the FloatImage-specialised versions under the original names. If t= his doesn't sound like a convincing approach, the Eigen library is a be= autiful example (I'm not sure whether it is the result of a refactor or= of some brilliant foresight).

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