RE: [sv-bc] 4.10.4 "Enumerated types in numerical expressions" - unclearness

Hi,

See below.

>In SystemVerilog, there are too many types to make this
>approach practical.
>What was needed was a concise generic term for the value to be
>used in these
>situations.  Since the most obvious place where this value is
>used is the
>default initial value of a variable, the term "default initial
>value" came
>into use.  And as the standard was clarified and new situations
>needing an
>"undefined" value were identified, they were generally defined
>to use this
>"default initial value".


[Shalom: ] The phrase "default initial value" is actually only used in a
small number of places:

- Here in 4.10.4.3 and 4.10.4.4, regarding enumeration next() and prev
()
- In 4.11, p. 30, with respect to a variable of an unpacked union type
- In 5.6.1, with respect to dynamic arrays
- In 5.9.6, with respect to non-existent members of associative arrays
- In 5.13, in a similar context
- In 5.14.1, in a similar context with respect to queues
- In Table 6-1 with respect to variables
- In 19.12.1, with respect to variables

Thus the phrase used in 4.10.4.3 and 4.10.4.4 as it currently stands is
at best not well defined. The "default initial value" of an
"enumeration" is not well defined. What is defined is the "default
initial value" of an enumeration variable, which is not the same thing.


>When some of the new data types were allowed on nets, this
>phrase became
>less accurate.  It really should have become "default initial
>value for
>a variable of this type", but that is no longer concise and may
>even be
>more confusing.  Perhaps these places should have been changed
>to say
>"the value from Table 6-1".

[Shalom: ] I am not sure that in the case of enumerations, "the value
from Table 6-1" would be unambiguous. For enumerations, Table 6-1 says,
"base type default initial value". But that brings us back to the
original question, as "default initial value" is defined for variables,
not for types. 

You might have to say something like "default initial value for a
variable of the base type".

Since Table 6-1 does not apply to nets, it might be wise to avoid saying
"default initial value" of a type, but rather "of a variable of this
type", as you said, even though you have some reservations about it.

Thanks,
Shalom