In The Pragmatic Programmer:
Normally, you can simply hide a third-party product behind a
well-defined, abstract interface. In fact , we've always been able to
do so on any project we've worked on. But suppose you couldn't isolate
it that cleanly. What if you had to sprinkle certain statements
liberally throughout the code? Put that requirement in metadata, and
use some automatic mechanism, such as Aspects (see page 39 ) or Perl,
to insert the necessary statements into the code itself.
Here the author is referring to Aspect Oriented Programming and Perl as tools that support "automatic mechanisms" for inserting metadata.
In my mind I envision some type of run-time injection of code. How does Perl allow for "automatic mechanisms" for inserting metadata?
Skip ahead to the section on Code Generators. The author provides a number of examples of processing input files to generate code, including this one:
Another example of melding environments using code generators happens when different programming languages are used in the same application. In order to communicate, each code base will need some information in commondata structures, message formats, and field names, for example. Rather than duplicate this information, use a code generator. Sometimes you can parse the information out of the source files of one language and use it to generate code in a second language. Often, though, it is simpler to express it in a simpler, language-neutral representation and generate the code for both languages, as shown in Figure 3.4 on the following page. Also see the answer to Exercise 13 on page 286 for an example of how to separate the parsing of the flat file representation from code generation.
The answer to Exercise 13 is a set of Perl programs used to generate C and Pascal data structures from a common input file.
Related
I've used lettuce for python in the past. It is a simple BDD framework where specs are written in an external plain text file. Implementation uses regex to identify each step, proving reusable code for each sentence in the specification.
Using scala, either with specs2 or scalatest I'm being forced to write the the specification alongside the implementation, making it impossible to reuse the implementation in another test (sure, we could implement it in a function somewhere) and making it impossible to separate the test implementation from the specification itself (something that I used to do, providing acceptance tests to clients for validation).
Concluding, I raise my question: Considering the importance of validating tests by clients, is there a way in BDD frameworks for scala to load the tests from an external file, raising an exception if a sentence in the test is not implemented yet and executing the test normally if all sentences have been implemented?
I've just discovered a cucumber plugin for sbt. Tests would be implemented under test/scala and specifications would be kept in test/resources as plain txt files. I'm just not sure on how reliable the library is and if it will have support in the future.
Edit:
The above is a wrapper for the following plugin wich solves perfectly the problem and supports Scala.
https://github.com/cucumber/cucumber-jvm
This is all about trade-offs. The cucumber-style of specifications is great because it is pure text, that easily editable and readable by non-coders.
However they are also pretty rigid as specifications because they impose a strict format based on features and Given-When-Then. In specs2 for example we can write any text we want and annotate only the lines which are meant to be actions on the system or verification. The drawback is that the text becomes annotated and that pending must be explicitly specified to indicate what hasn't been implemented yet. Also the annotation is just a reference to some code, living somewhere, and you can of course use the usual programming techniques to get reusability.
BTW, the link above is an interesting example of trade-off: in this file, the first spec is "uglier" but there are more compile-time checks that the When step uses the information from a Given step or that we don't have a sequence of Then -> When steps. The second specification is nicer but also more error-prone.
Then there is the issue of maintaining the regular expressions. If there is a strict separation between the people writing the features and the people implementing them, then it's very easy to break the implementation even if nothing substantial changes.
Finally, there is the question of version control. Who owns the document? How can we be sure that the code is in sync with the spec? Who refactors the specification when required?
There is no, by far, perfect solution. My own conclusion is that BDD artifacts should be in the hand of developers and verified by the other stakeholders, reading the code directly if it's readable or reading an html/pdf output. And if the BDD artifacts are owned by developers they might as well use their own tools to make their life easier with verification (using a compiler when possible) and maintenance (using automated refactorings).
You said yourself that it is easy to make the implementation reusable by the normal methods Scala provides for this kind of stuf (methods, functions, traits, classes, types ...), so there isn't really a problem there.
If you want to give a version without code to your customer, you can still give them the code files, and if they can't ignore a little syntax, you probably could write a custom reporter writing all the text out to a file, maybe even formatted with as html or something.
Another option would be to use JBehave or any other JVM based framework, they should work with Scala without a problem.
Eric's main design criteria was sustainability of executable specification development (through refactoring) and not initial convenience due to "beauty" of simple text.
see http://etorreborre.github.io/specs2/
The features of specs2 are:
Concurrent execution of examples by default
ScalaCheck properties
Mocks with Mockito
Data tables
AutoExamples, where the source code is extracted to describe the example
A rich library of matchers
Easy to create and compose
Usable with must and should
Returning "functional" results or throwing exceptions
Reusable outside of specs2 (in JUnit tests for example)
Forms for writing Fitnesse-like specifications (with Markdown markup)
Html reporting to create documentation for acceptance tests, to create a User Guide
Snippets for documenting APIs with always up-to-date code
Integration with sbt and JUnit tools (maven, IDEs,...)
Specs2 is quite impressive in both design and implementation.
If you look closely you will see the DSL can be extended while you keep the typesafe-ty and strong command of domain code under development.
He who leaves aside the "is more ugly" argument and tries this seriously will find power.
Checkout the structured forms and snippets
Are there any tools which diff hierarchies?
IE, consider the following hierarchy:
A has child B.
B has child C.
which is compared to:
A has child B.
A has child C.
I would like a tool that shows that C has moved from a child of B to a child of A. Do any such utilities exist? If there are no specific tools, I'm not opposed to writing my own, so what are some good algorithms which are applicable to this problem?
A great general resource for diffing hierarchies (not specifically XML, HTML, etc) is the Hierarchical-Diff github project based on a bit of Dartmouth research. They have a pretty extensive list of related work ranging from XML diffing, to configuration file diffing to HTML diffing.
In general, actually performing diffs/patches on tree structures is a fairly well-solved problem, but displaying those diffs in a manner that makes sense to humans is still the wild west. That's double true when your data structure already has some semantic meaning like with HTML.
You might consider our SmartDifferencer tools.
These tools compare computer source code files in a diff-like way. Unlike diff, which is line oriented, these tools see changes according to code structure (variable name, expression, statement, block, function, class, etc.) as plausible edits ("move, insert, delete, replace, copy, rename"), producing answers that makes sense to programmers.
These computer source codes have exactly the "hierarchy" structure you are suggesting; the various constructs nest. Specifically to your topic, typically code blocks can nest inside code blocks. The SmartDifferencer tools use target-language accurate parsers to "deconstruct" the source text into these hierarchical entities. We have a Smart Differencer for XML in which you can obviously write nested tags.
The answer isn't reported as "Nth child of M has moved" although it is actually computed that way, by operating on the parse trees produced by the parsers. Rather it is reported as "code fragment of type at line x col y to line a col b has moved/..."
The answer my good sir is: Depth-first search, also known as Depth-first traversal. You might find some use of the Visitor pattern.
You can't swing a dead cat without hitting some sort of implementation for this when dealing with comparing XML trees. Take a gander at diffxml for an example.
Whenever I see the term source filter I am left wondering as to what it refers to.
Aside from a formal definition, I think an example would also be helpful to drive the message home.
A source filter is a module that modifies some other code before it is evaluated. Therefore the code that is executed is not what the programmer sees when it is written. You can read more about source filters (in the Perl context) at perldoc perlfilter. Some examples are Smart::Comments which allows the programmer to leave debugging commands in comments in the code and employ them only if desired, another is PDL::NiceSlice which is sugar for slicing PDL objects.
Edit:
For more information on usage (should you wish to brave the beast), read the documentation for Filter::Simple which is a typical way to create filters.
Alternatively there is a new and different way to muck about with the source: Devel::Declare lets you interact with Perl's own parser, letting you do many of the same type of thing as a source filter, but without the source filter. This can be "safer" in some respect, yet it has a more limited scope.
A source filter is a form of module which affects the way in which a file use-ing it will be parsed. They are commonly used to simulate syntactical features which Perl does not have natively -- for instance, the Switch source filter was often used to simulate switch statements before Perl's given { } construction was available.
Source filters work by taking the text of the module as input, performing some processing on it, and outputting the filtered source code. For a simple example of how a source filter is implemented, as well as more details, see the perldoc page for perlfilter.
They are pre-processors. They change the source code before it reaches the Perl compiler. You can do scary things with them, in effect implementing your own language, with all the effects this has on readability (for others), robustness (writing parsers is hard) and maintainability (debugging gets tricky when your idea of what the source code is differs from what compiler and runtime think it is).
I have the following question:
Let's assume I have many different C++ libraries(algorithms), which are written in the same style . (They need some inputs and give back some outputs).
I've done some research and wanted to ask if its possible to auto-generate Wrapper classes (by using an algorithm which are given the input and the outputs of the c++ algorithm), which can be easily used in Objective-C/Java (iOS/Android) then .
The app-programming part isn't really time-consuming.
You'll want to look at SWIG. This generates bindings for other languages from a C based API. Objective-C support is in there as is Java.
I'm not sure what happened to objective-C support in the later versions, but its in v1.1 and you can see the branch where it was added.
I use CodeSmith for the PLINQO templates, to build my DAL from my DB objects; it works great!
I believe that's the primary use of code generator apps, but I'm curious... what other code would you consider using a code generator for? Do you have any CodeSmith templates that you use frequently (if so, what does it do)?
I haven't used CodeSmith, but I've done a fair bit of code generation. Noteably I wrote most of a configuration management (CM) system for a WiMAX system, where the CM code was generated for 3 different platforms. The only difference was the CM model for each platform.
The model was in a custom Domain Specific Language (DSL) that we built had a parser for. The language was a basic container/element style where containers could nest and have an identifier, and elements were of pre-defined types. Documentation was an attribute of elements and containers. You could add Lua snippets to the element and container definitions to do semantic validation (e.g., the value is in the correct range, if it's an IP address is it in a CIDR range defined elsewhere, etc.).
The parser generated a syntax tree that we then pushed at templates. The template language was a partial C implementation of StringTemplate. We used it to generate:
A model specific C API that applications could call into to get configuration values,
The collected Lua code for validating the model and providing useful error messages,
Two "backends" for the API that would manage values in memory (for temporary manipulation of a model), and in a database system (for sharing amongst processes),
Configuration file parser and writer,
HTML documentation, and
Command Line Interface (CLI) implementation for interactive viewing and changing of a configuration.
In retrospect, I should have simply used Lua directly as the DSL. It would have been more verbose, but having the parser already there and lots of Lua templating choices available to me would have saved a lot of development effort.
For things that have a repetivie structure and well defined rules about what those things need to do, code generation can be a wonderful thing.