Stata Conference 2023 - Metaprogramming

Metaprogramming

What it is, how to use it, and why you should care

Billy Buchanan

Sr Research Scientist, SAG Corporation

Service Disabled Veteran Owned Small Business Emblem

Slides available at: https://wbuchanan.github.io/stataConference2023

What it is

Programs that write or modify programs
Inputs are data, metadata, and/or sourcecode
Processes Concept Classes used (see Damaševičius & Štuikys, 2008 for details):

Code Generation
Transformation
Reflection
Generalization

Output is static or dynamic

How is it implemented in Stata?

Macros

Macros can be used to compose syntax
Evaluation of macros enables flexible composition
Control evaluation with \ or macval()
Access metadata with extended macro functions

Mata Strings

Use string variables to create and modify syntax
Incorporate values stored in Stata macros as needed
Mata function stata() can execute your code
Mata classes persist across Stata commands

How to use it

Dynamic Code Generation

Static Code Generation

Transformation

Code Templates

Code Templates

Stata/Java "Reflection"

I'll show a use of reflection for method dispatch that saved a fair amount additional effort
Here is what would have needed to take place in the body of each method without using any form of metaprogramming:

Instantiate the object for the specific string encoding
Add the variable to Stata
Get the variable index for the new variable from Stata
Create a string joiner for the observation
Loop over the user specified variables to construct the string over one or more variables
Call the method that returns the phonetic encoding on the string and insert back into Stata

Instead, each method calls a single meta method and passes a class name to it along with the name for the new variable.
The meta method uses a concept called reflection to instantiate which ever type of object is needed and to identify and call the appropriate method on that object to encode the string.

Why you should care

Abstraction
Time Savings
Automation/Reproducibility

Remember

Programs that write or manipulate other programs
Use macros and Mata strings variables
Proper use = reduced time and effort