[[C++ PATCH]] Implement C++2a P0330R2 - Literal Suffixes for ptrdiff_t and size_t

[Ed Smith-Rowland <3dw4rd at verizon dot net>]

All,

This patch implements C++2a proposal P0330R2 Literal Suffixes for 
ptrdiff_t and size_t*.  It's not official yet but looks very likely to 
pass.  It is incomplete because I'm looking for some opinions. 9We also 
might wait 'till it actually passes).

This paper takes the direction of a language change rather than a 
library change through C++11 literal operators.  This was after feedback 
on that paper after a few iterations.

As coded in this patch, integer suffixes involving 'z' are errors in C 
and warnings for C++ <= 17 (in addition to the usual warning about 
implementation suffixes shadowing user-defined ones).

OTOH, the 'z' suffix is not currently legal - it can't break 
currently-correct code in any C/C++ dialect.  furthermore, I suspect the 
language direction was chosen to accommodate a similar addition to C20.

I'm thinking of making this feature available as an extension to all of 
C/C++ perhaps with appropriate pedwarn.

Opinions?

Ed Smith-Rowland

[*] http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2018/p0330r2.html

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