Exploringmetaprogramming

using Ruby language

A brief introduction

Harshal Ganpatrao HayatnagarkarPhD Candidate in Dept. of Computer Science

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Friday, October 3, 2014

Engineering marvels

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Ford Model T (approx. 1918) Tesla Model S (2010)

Assembly Lines: Process marvels

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Ford Model T Assembly Line

Tesla Robotic Assembly Line

Assembly Lines: Process marvels

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People building robots build robots building cars

What is this analogous to?

People building carsA worker on assembly line does same task repetitively, item after item and day after day.

People building robots building carsIs this like programming?

Courtesy: http://stackoverflow.com/questions/3468246/whats-the-use-of-metaprogramming

Metaphor

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People building robots building robots… building carsWhat is this analogous to?

…

Meta-programming

• Meta (‘beyond’ in Greek) + programming Programming Abstraction– Similar to meta-data, meta-model, meta-physics and so on.

• “Writing of computer programs that with ability to treat programs as their data, as it meant that a program could be designed to read, generate, analyse and/or transform other programs, and even modify itself while running. In some cases, this allows programmers to minimize the number of lines of code to express a solution (hence reducing development time), or it gives programs greater flexibility to efficiently handle new situations without recompilation.” - Wikipedia

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Revelation

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Data-Code Duality

Two aspects

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Reflection Generative programming

Reflection

• Ability of a computer program to examine and modify the structure and behavior (specifically values, meta-data, properties and functions) of the program at runtime.– Metalanguage in which metaprogram is written. – object language, programs written in which are manipulated.– reflection or reflexivity is ability of a programming language to

be its own metalanguage.

• Fairly common in programming languages– C++ (limited)– Java (+ other JVM languages), C# (+ other CLR languages)– JavaScript, Python, PHP, Ruby

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Generative Programming

• “A style of computer programming that uses automated source code creation through generic frames, classes, prototypes, templates, aspects, and code generators to improve programmer productivity.” - Wikipedia

• For example, – Internal to language: C/C++ preprocessor macros, C++

templates, LISP macros, Ruby/Python/PHP evaluations.

– External: Code generation templates.

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Ruby Programming Language

• Dynamic, reflective, object-oriented, general-purpose programming language.

• Influenced by Perl, Smalltalk, Eiffel, Ada, and Lisp.

• Supports multiple paradigms functional, object-oriented, and imperative.

• With dynamic type system and automatic memory management.

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Yukihiro "Matz" Matsumoto

Meta Object Protocol

• Everything is an object, including classes.

• Method calling is analogous to message passing where arguments are payload.

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Open Classes

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Dynamic methods

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Dynamic methods

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Ruby on Rails – ActiveRecord example

Generative Programming

• Code generation – one or more levels– ‘eval’ expression family– Takes source code in string form and embed in current

context.

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Two-level generation• Code generating code generating code

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Level 1

Level 2

‘Level 1’ eval

‘Level 2’ eval

Pitfalls

• Metabugs?– Bugs generating bugs generating…

– And there is no ‘programs debugging programs debugging programs…’.

• Increased code complexity

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Further exploration…

• Model-driven development

• Domain-specific languages

• Ruby on Rails for web development framework

– An example of metaprogramming features.

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Questions?

And thank you for your interest !

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