🚀 go-pugleaf

clamage@Eng.Sun.COM (Steve Clamage) writes:

>David Byrden <100101.2547@compuserve.com>
>writes:
>>Why, in the Septenber draft standard, is an allocator-specific verrion of 
>>'new' provided;
>>
>>20.1.4.4
>>
>>           new(x) T    
>>
>>    returns an X::types<T>::pointer, where x is of an 
>>    allocator type X
>
>You are actually referring to the "placement new" syntax not having a
>corresponding "placement delete" syntax.

No; that's part of the issue, but there is also a question of why
allocators are not required to define an operator delete() function.
If I write

	new (x) T

where x is an allocator, and the constructor for T throws an
exception, does x.deallocate() get called?  According to the
September draft, I don't think it does -- and that is a real
problem.

There also appears to be another problem with

	new (x) T[n];

The supposed semantics of this are

	new((void*)x.template allocate<T>(n)) T[n]

However, that may have undefined behaviour!
The reason is that it may not allocate enough memory.
It is only guaranteed to allocate enough memory to hold
`n' objects of type `T'.  However, the compiler
need additional space for ``array allocation overhead''
(see [expr.new]).

--
Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3
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