CODEWITHSUNDEEP
specman
user3444042
user3444042

Reputation: 21

what is the difference between 'define as' to 'define as computed' in specman?

The difference between the two is not so clear from the Cadence documentation. Could someone please elaborate on the difference between the two?

Upvotes: 1

Views: 501

Answers (2)

Yuri Tsoglin
Yuri Tsoglin

Reputation: 963

With both define as and define as computed macros you define a new syntactic construct of a given syntactic category (for example, <statement> or <action>), and you implement the replacement code that replaces a construct matching the macro match expression (or pattern). In both cases the macro match expression can have syntactic arguments that are used inside the replacement code and are substituted with the actual code strings used in the matched code.

The difference is that with a define as macro the replacement code is just written in the macro body. With a define as computed macro you write a procedural code that computes the desired replacement code text and returns it as a string. It's effectively a method that returns string, you can even use the result keyword to assign the resulting string, just like in any e method. A define as computed macro is useful when the replacement code is not fixed, and can be different depending on the exact macro argument values or even semantic context (for example, in some cases a reflection query can be used to decide on the exact replacement code). (But it's important to remember that even define as computed macros are executed during compilation and not at run time, so they cannot query actual run time values of fields or variables to decide on the resulting replacement code).

Here are some important differences between the two macro kinds.

  • A define as macro is more readable and usually easier to write. You just write down the code that you want to be created.
  • Define as computed macros are stronger. Everything that can be implemented with define as, can also be implemented with define as computed, but not vice versa. When the replacement code is not fixed, define as is not sufficient.
  • A define as macro can be used immediately after its definition. If the construct it introduces is used in the statement just following the macro, it will already be matched. A define as computed macro can only be used in the next file, and is not usable in the same file in which the macro is defined.

Upvotes: 1

Tudor Timi
Tudor Timi

Reputation: 7573

A define as macro is just a plain old macro that you probably know from other programming languages. It just means that at some select locations in the macro code you can substitute your own code.

A define as computed macro allows you to construct your output code programmatically, by using control flow statements (if, for, etc.). It acts kind of like a function that returns a string, with the return value being the code that will be inserted in its place by the pre-processor.

Upvotes: 1

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