Re: [boost] Proposal for #pragma once support

Subject: Re: [boost] Proposal for #pragma once support
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-06-11 10:46:33

Stephen Nuchia wrote
On Wednesday, June 10, 2009 10:46 AM
>
> #pragma once is useful in Windows for the same reason they have the
> pre-compiled header abomination: slow directory-level file system
> operations and a really bad system header legacy.
>
> On the point that some headers should not use this mechanism:
> in addition to headers designed to instantiate something in-
> place, some headers include optional components activated by a
> user-specified define.  The idempotent and flag-independent
> portions can be enclosed in a preprocessor include guard but
> the optional part should be left outside the guard.

[snip examples of optional code outside guard]

[snip examples of Microsoft magic speedup mechanisms]

These all just reinforce the idea that an automated solution is only a first pass.  Building and testing must occur to find the headers that should not use #pragma once before the changes are committed, assuming this effort comes to fruition.  Since making the changes, building successfully, and testing successfully, must occur in order to provide meaningful test results, special cases like those you've noted will have been addressed.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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