Introduction to Eiffel
Suppose you need a class to manipulate a structured collection of objects—an array of INSECTs, a parse tree, a hashed list of sales prospects, or some such thing?
Some object-oriented languages furnish a general approach. You construct a template for, say, a LINKED_LIST or an ARRAY. You then use this template with some arguments indicating the classes to be used in constructing the particular LINKED_LIST or whatever.
In Eiffel, this capability is called genericity, and the templates are generic classes. As usual, this is done in a way that does the job and yet is so simple, it seems effortless.
Suppose you are writing an ant hill. First you need some ants.
class ANT inherit INSECT -- A basic ant. It has features to crawl, -- forage, dig, tend the young, and so on. ... end class CARPENTER_ANT inherit ANT redefine -- Redefine some things. -- These chew on your house and your apple -- tree. ... end; ... end class ARMY_ANT inherit ANT redefine -- These are always on the go. -- You hope they don't stop by your place -- for dinner. ... end; ... end
Now you are ready for ant hills. Let us suppose you already have some class that models insect societies. Its header might look like this
class INSECT_SOCIETY[G->INSECT] ...
which indicates that an INSECT_SOCIETY may be formed using a parameter that conforms to INSECT. Loosely, this means any descendent INSECT will do. anthill:INSECT_SOCIETY[ANT] declares a reference to an INSECT_SOCIETY containing ants. This reference may then be attached an INSECT_SOCIETY containing CARPENTER_ANT, ARMY_ANT, or any other descendent of ANT we have defined. In fact, this allows us to reference an anthill comprising more than one kind of ant, which is convenient, as some anthills may contain more than one kind of ant.
In writing a specific container class, for example, we may wish to take advantage of things we know about insects in the features of the container class. It would never do, in such a situation, for example, to enter an object of class DOG or HAMMER into this container. The type-safe mechanism for doing this is called constrained genericity and is illustrated above in the header line for class INSECT_SOCIETY.
The Eiffel programming language offers power, simplicity, strong type checking, and numerous other amenities. With an open specification for both the language and the kernel libraries, and support from multiple vendors, Eiffel now stands poised to take off.
According to one vendor, most interest lately has come from people who are turning to Eiffel having used C++ for some years and who have become convinced that the training costs and the complexity of that language are not justified by the features provided.
The more adventurous among us who have a thirst to tackle an object-oriented programming language unhindered by excess baggage from the past ways of doing things may wish to further explore this language.
In my next article, I'll write more about ISE Eiffel and the compiler and tools from Tower Technology of Austin, Texas. I'll also offer a few thoughts about how to get started with this language.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide