Location/Rationale of generated code

[Juan Manuel]

I am using Rhino for a research project, and I need to understand certain parts of the system.

I came across the switch statement in https://github.com/mozilla/rhino/blob/master/src/org/mozilla/javascript/TokenStream.java#L167 and I am very curious about it. I have two questions:

1. It seems to be generated code but I can't seem to find how it is generated. Where is the logic that generates this code?
2. What is the rationale for using this switch instead of simply using a set with the keywords, for example?

Thank you.

[Gregory Brail]

That's a fun one, and it's used all over Rhino.

The code is generated by "idswitch" -- the source is in the "tools" directory. 

It is used in every native Rhino class that needs to look up a property name from a string, and does so more efficiently than a long sequence of individual string comparisons.

The Rhino codebase dates back to the earliest days of Java, and I presume that back then this type of generated code made a meaningful performance difference versus, say, a static hash table. It'd be fun to do some research and see if that's still the case.

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[Juan Manuel]

Thank you! That's very interesting, I didn't realize Rhino was that old

On Thursday, July 25, 2019 at 4:12:18 PM UTC-4, Gregory Brail wrote:

That's a fun one, and it's used all over Rhino.

The code is generated by "idswitch" -- the source is in the "tools" directory. 

It is used in every native Rhino class that needs to look up a property name from a string, and does so more efficiently than a long sequence of individual string comparisons.

The Rhino codebase dates back to the earliest days of Java, and I presume that back then this type of generated code made a meaningful performance difference versus, say, a static hash table. It'd be fun to do some research and see if that's still the case.

On Thu, Jul 25, 2019 at 10:57 AM Juan Manuel <jmflo...@gmail.com> wrote:

I am using Rhino for a research project, and I need to understand certain parts of the system.

I came across the switch statement in https://github.com/mozilla/rhino/blob/master/src/org/mozilla/javascript/TokenStream.java#L167 and I am very curious about it. I have two questions:

1. It seems to be generated code but I can't seem to find how it is generated. Where is the logic that generates this code?
2. What is the rationale for using this switch instead of simply using a set with the keywords, for example?

Thank you.

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