Re: [boost] metactrl header [was Smart Pointer...]

From: jsiek_at_[hidden]
Date: 2000-07-21 17:37:09

Right, the meta_assert is good when you can express the check as some
expression convertible to bool. The mechanisms in concept_checks.h are
more for ensuring that the components that get plugged-together really
do what they are suppose to.

BTW, the lambda library uses a ct_assert which is the same as
meta_assert.

Cheers,

Jeremy

Beman Dawes writes:
 > Well, it got me going:-)
 > 
 > How about something a bit simpler:
 > 
 >      template<bool Pred> struct meta_assert
 >         { int assertion_failure_in_meta_assert[Pred ? 1 : -1]; };
 > 
 >      template<> struct meta_assert<true> {};
 > 
 > This actually works for BCC, MWCW, and MSVC compilers.  The specialization 
 > has to be the <true> flavor for some of them.  Steve Cleary introduced me 
 > to the negative subscript trick, IIRCC.  Kevlin Henney has used a similar 
 > (or maybe the same?) technique in other boost postings.
 > 
 > The usage inside a generator (where b is a compile time expression 
 > convertible to bool) is:
 > 
 >     meta_assert< b > use_name_as_error_message_surogate;
 > 
 > It could also be used as a base class, but I haven't tested that.
 > 
 > Would this be sufficient for template metaprogramming?
 > 
 > --Beman
 > 
 > 
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