wharfinger's New Writeups

Join (idea)

2002-02-25T20:33:28Z

Join is an SQL ("Structured Query Language") keyword. SQL is a language used to talk to databases.

A join operation creates a temporary database table or "record set", composed of elements of two existing tables. There are a few different ways you might go about joining. In all cases, each record in the new table is composed of at most one record from each of the two tables being joined. Your join statement will say how the database should decide which records go together. You can think of a "record" as a "row" much like in a spreadsheet such as Excel, and a "field" as a "column" (again, as in a spreadsheet).

You can also take the result of one join operation, and join that with another table, or with the result of another join operation.

We'll define two very small tables and use those for each example. Even though SQL is case-blind, we'll use all caps for keywords so they stand out clearly. Each of these examples begins with "SELECT *…

pointer semantics (thing)

2002-02-24T23:37:18Z

When we do object oriented programming, some class instances represent things that are rather large.

There are two ways of looking at such a class: One is that it is or contains the representation of whatever it's representing. A string, for example. We call that "value semantics". If you make a copy of an object with value semantics, you get a copy of the whole thing: That's what copying "means" for that class; that's why we call it "semantics".

The other approach is "pointer semantics": The object you have in your hand is to be thought of as a reference to the data. If you make a copy of an object with pointer semantics, the "meaning" of that operation is like making a copy of a pointer: You get a new, and quite compact, reference to the same old thing.

The "pointer semantics" approach is common with string classes. Many instances of a pointer-semantical class can share the same data "inside". Naturally, you need to implement a…

Cascading Style Sheets (idea)

2002-02-24T15:45:25Z

Cascading style sheets are, or more properly is, a standard defined and promulgated ("huh huh, he said 'promulgated'!") by the World Wide Web Consortium or W3C. As of this writing (February, 2002), the W3C's CSS "home page" is a virtually unusable mess located at http://www.w3.org/Style/CSS/. That page is not the worst example of malignant CSS abuse that I've seen, but it'll do.

Most people use the abbreviation CSS for the sake of convenience. In theory, CSS should separate presentation details from document structure: Tags "should" be used only if they have some logical meaning. Sheer decoration "should" be done with CSS. In practice, there's no good place to draw the line. Ideally, we'd do everything in XML with appropriate DTDs and convert it into HTML on the fly, but like all software development everybody's got a deadline and it's just a mess. Any discussion of the issue degenerates rapidly into hair-splitting and holy wars.

The current (Feb…

root log: February 2002 (thing)

2002-02-23T23:54:52Z

Except for the first one, this is mostly flash stuff that has little impact on functionality.

Added the collaboration nodetype. It's essentially a document with an access control list and with locking. CEs and gods have full access and can forcibly unlock. Locks expire after 15 minutes from last submit.

It also supports the imaginary <highlight> tag which is s//'d into <span class="oddrow"> when the text is displayed. Is there a real tag that would be appropriate for that? I can't find one; <del> is as close as it gets.

I guess I'll also add a switch to hide text in highlight tags.

This feature matters. crtleads will in time be given access like that of CEs. Even now, we have a workable mechanism for users to collaborate on writing. Previously, this could be done only if one of the collaborators was a CE, and it had to go in a writeup, which is sucky for a number of reasons.

…

wild geese (thing)

2002-02-19T23:53:23Z

Even on dry days, you don't dare sit on the grass.

A small flock of Canada geese has chosen to winter at our office park in Massachusetts. It's been warm this year and we've had very little snow. They seem fat enough, but it's hard to say. It's only late February. They should have been on their way south long since. The geese waddle around the buildings, pulling at the grass with their bills and looking for something to eat. They wander back and forth across the parking lot between the buildings and the woods. Sometimes when I'm driving in or out, I have to stop and let them pass. They're in no hurry. In the summer, we have chipmunks and squirrels. I worry more about hitting the mammals because they're harder to spot, but at least they keep up the pace and get out of your way.

Lately the geese have been spending their time in front of the building, under a pair of sizable oak trees and some ratty bushes. When I go outside to smoke, the geese look at me…

pure virtual (thing)

2002-02-17T18:04:11Z

If you know some C++ but you're not sure what a virtual function is, please read that one first. If you don't know C++ at all, read Halspal's stuff instead. He's really good.

In the C++ programming language, a "pure virtual" function is a class member function which is declared but not implemented. It is, of course, declared virtual. If you call a pure virtual function, your program will crash, because there's no function there. It turns out that calling a pure virtual is possible, and even fun, if that's your idea of fun¹.

You declare a pure virtual function by putting "= 0" at the end of the declaration of a virtual function:

    class foo {
        virtual void bar() = 0;
    }

We write pure virtual functions in cases where we want to specify an interface which will be inherited by a subclass, but we are unable and unwilling to specify anything about the implementation…