[RFC] [PATCH] Add __array_size keyword

[Joseph Myers]

On Thu, 11 Feb 2016, Stuart Brady wrote:

> Documentation and test code are currently absent from the patch, but I

For proposed features, I find documentation and testcases of much more 
value than the rest of the implementation.  Critical issues to define and 
cover thoroughly in tests include the rules for when operands of sizeof 
are evaluated, as adapted appropriately for this keyword, and for when it 
returns various kinds of constants.  Is the rule for your keyword that the 
operand is evaluated, and the result not an integer constant, iff the 
operand is an array with a variable number of elements (as opposed to an 
array with a constant number of elements that themselves are 
variable-sized, for example)?  C11 6.5.3.4#2 (sizeof) would need testing, 
but so would 6.9#3 (rules about when declared identifiers need to be 
defined), and 6.6#6 and #8 (constant expressions) - and anything else in 
C11 that mentions sizeof.  Presumably this keyword can be applied to an 
array at function prototype scope whose size is explicitly or implicitly 
[*], though nothing useful can be done with the results, as with [*]?  
(Cf. gcc.dg/vla-5.c.)

-- 
Joseph S. Myers
joseph@codesourcery.com