Re: [sv-ec] String proposal

Shalom,

I think you raise a good point. I'll try to clarify what is meant and perhaps you can suggest
improvements to the language.

I believe the confusion regarding string being used as a noun or as an adjective
stems from the fact that there are now three kinds of strings in the language:
    string literals - the traditional double-quote enclosed literal values denoting ASCII strings
    string types - the new variable-size type that acts as a string container
    string variables - variables of type string (the above type).

When it refers to a string literal, the text is explicit about using the full term. When it refers to
string types or string variables, the noun "type" or "variable" is often excluded. I think that part
of the confusion is due to not having merged the P1800 and 1364 LRM's into one document.
When that happens, we will have to reconcile the terms much better. I believe the SystemVerilog
usage is consistent with the fact that a 1364 string is really a literal value (after all they are defined
as part of the lexical conventions and cannot be modified). Given that there is now a built-in type
whose actual name is "string", I think it would be a mistake to continue to refer to string literals
as just "string". In my opinion, this has to change.

Let me take some of the items you mention:

"Reading an element of a string yields a byte. A string shall not contain the special character \0 ."

How about:
 
"Reading one element of a string variable yields a byte. A string variable shall not contain the special character \0 ."
----------------

"A string or a string literal can be assigned directly to a string variable."

"A string variable or a string literal may be assigned directly to a string variable."
----------------

bit [11:0] b = 12'ha41;
string s2 = string'(b); // sets s2 to 'h0a41

'h0a41 is an unsized constant and thus at least 32 bits.
You probably mean 16'h0a41.

Yes. that's better.
-----------------

- "b = string'(r) ; // OK (implicit cast, implementations can issue a warning)"

"can" should probably be "may".

Yes.
-----------------

r = {"H",""}; // yields "H\0" "" is converted to 8'b0
b = {"H",""}; // yields "H" as "" is the empty string

The comments are gramatically incorrect.
In the first, there probably should be a period between "H\0" and "".
I don't know about the second.

Yes, I believe you're right. How about:
r = {"H",""}; // yields "H\0". "" is converted to 8'b0
b = {"H",""}; // yields "H". "" is the empty string
----------------

Now I'm confused again.
What is the result of a[0] = "hi", where a is of type string?

Yes. That is still a pending errata, which I have no doubt we will change to
be compatible with other assignments so that:
    a[0] = "hi";
assigns "i" to a[0] , same as a[0] = "i"

    Arturo

----- Original Message -----
From: <Shalom.Bresticker@freescale.com>
To: "Arturo Salz" <Arturo.Salz@synopsys.COM>
Cc: "sv-ec" <sv-ec@eda.org>
Sent: Monday, December 06, 2004 10:39 PM
Subject: Re: [sv-ec] String proposal

Arturo,

I don't understand all of this, but I still have a few comments.

- The term "string" when used as a noun and not as an adjective is not
always clear. The usage appears to be inconsistent.

For example, in the sentences,
"Reading an element of a string yields a byte. A string shall not contain the special character \0 ."

What types of strings are meant here?

Or afterward,

"A string or a string literal can be assigned directly to a string variable."

What is the difference between a string and a string literal?

("can" should probably be "may".)

Note especially that for better or for worse, in 1364, the term "string" is defined as
"A string is a sequence of characters enclosed by double quotes ("") and contained on a single line."

I think the current usage of string as a noun without any adjective is confusing and inconsistent.

- You have

bit [11:0] b = 12'ha41;
string s2 = string'(b); // sets s2 to 'h0a41

'h0a41 is an unsized constant and thus at least 32 bits.
You probably mean 16'h0a41.

- "b = string'(r) ; // OK (implicit cast, implementations can issue a warning)"

"can" should probably be "may".

-
r = {"H",""}; // yields "H\0" "" is converted to 8'b0
b = {"H",""}; // yields "H" as "" is the empty string

The comments are gramatically incorrect.
In the first, there probably should be a period between "H\0" and "".
I don't know about the second.

- Question:
In:

a[0] = "h"; // OK. same as a[0] = "hi")

you deleted the second part of the comment (and forgot the closing parens).

The following statements still exists:

str.putc(i, s) replaces the ith character in str with the first character in s.
s can be any expression that can be assigned to a string.
Note: str.putc(j, x) is semantically equivalent to str[j] = x

Now I'm confused again.
What is the result of a[0] = "hi", where a is of type string?

Thanks,
Shalom

On Mon, 6 Dec 2004, Arturo Salz wrote:

> Plase find an attached proposal that specifies the interaction between string and zero characters.
>
> The proposal essentially disallows "\0" characters from being embedded in a string, and defines
> the rules for converting string literals to strings or casting integral values to a string.
>
> My apologies for the late notice.
>
> Arturo
>
>
>

-- 
Shalom Bresticker                        Shalom.Bresticker @freescale.com
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