Re: rep clause in generics

[dewar@merv.cs.nyu.edu (Robert Dewar)]

iJonas said

<<Element_Type'size is determined by a run-time parameter, so it is NOT
static.
>>

That's not the correct way to reason. Whether an expression is static or
not is NOT a question of whether the value is determined at run time or
not. There are lots of examples of values that are known at compile time
but are not static expressions. The rules on static expressions are in
RM 4.9. An expression is static iff the rules in 4.9 say it is static. period.

Now in this case, there is no rule that says this expression is static, but
the reasoning is confusing (for example, by this reasoning, one would expect
that 'Size applied to a digits formal should be static, because certainly
the size is known at compile time, since it is fixed for any particular
instantiation).

But this reasoning is faulty, as 4.9 shows, since x'size is still non-static
for a formal digits type x, since there is no rule that says it is static.