Specman 9.2 Preview: Shortened “When Subtype” Declarations

[Preface: all features in the 9.2 preview series are in Beta now. We invite you to sign-up for the beta program and give this feature a test drive!]

[Team Specman welcomes back Yuri Tsoglin from Specman R&D to introduce one of “his” new features.]

Abstract
The current syntax of "when" struct member declaration explicitly includes the base (parent) struct name, in the context of which it is evaluated. Starting in Specman 9.2, you do not need to explicitly mention the base type name, saving editing, compile, and run time, while also making the code more readable and easier to reuse.

Problem Statement
As some of you in the audience have pointed out in the past, the current “when subtyping” syntax is redundant because it requires you to include the base struct name in a "when" declaration although it is clearly implied by the context in which the "when" declaration appears. In fact, if the base struct name is different from that of the context, it causes an error message.

Solution Overview
This new short form of the when subtyping syntax is particulalry convenient for "when" declarations in template types, since a template type full name may be long, and it is more convenient to omit it when possible. Here is the new, official definition:

when struct-subtype [base-struct-type] {struct-member; ...}

The syntax and the meaning of the parameters are same as described currently in the docs (Section 4.7.1 of the Specman 8.2 “e_ref”), with the only modification: base-struct-type became optional. The following examples show the usage of the new syntax, with the existing syntax shown as a comment.

Example 1
The following struct contains when struct member declarations using the new short syntax.

<'
type color_t: [red, green, blue];
struct packet {
   color: color_t;
   good: bool;
   // when red packet {
   when red {
       size: int;
   };
   // when red good packet {
   when red good {
       print_msg() is {
           out("This is a red good packet, size = ", size);
       };
   };
};
'>

Example 2
The following example shows when struct member declarations using the new short syntax in a template type definition and in its instance extension.

<'
type color_t: [red, green, blue];
template struct map of (<key'type>,<value'type>){
   color: color_t;
   // when red map of (<key'type>,<value'type) {
   when red {
     print_msg() is {
       out("This is a red map.");
     };
   };
};

 extend map of (int(bits: 16), list of string) {
   // when red map of (int(bits: 16), list of string) {
   when red {
       print_msg() is also {
            out("It holds string lists, with 16-bit int keys.");
       };
   };
};

I hope you find this new syntax useful, and I invite you to send me any questions or feedback by posting a comment below, or forward them via Team Specman.

Happy Coding!

Yuri Tsoglin
Specman R&D