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  File System vs Core Data: the image cache test

Code for this project is on GitHub While doing a full re-write of Droplr's iOS app for the 2.0 launch, I couldn't find any good file/image caches out there had a particular feature I really wanted: extending item expiration whenever it's touched. I set out to write my own — which wasn't that much of a challenge — but somewhere along the process I had this crazy idea that perhaps (SQLite-backed) Core Data would be a much better tool for the job: No mismatch between cache index ...

   File system.Image cache,Multimedia     2012-02-01 08:52:02

  Lisp: It's Not About Macros, It's About Read

Note: the examples here only work with outlet lisp. Refer to your version of lisp/scheme’s documentation for how read works (and possibly other forms) I know it’s an old post by now, but something about the article Why I love Common Lisp and hate Java, part II rubbed me the wrong way. The examples just aren’t that good. The usage of macros is plain baffling, when a function would have been fine. The author admits this, but still does it. There’s a follow-up post wh...

   Lisp,Macro,Read,Java     2012-02-19 06:12:19

  Understanding lvalues and rvalues in C and C++

The terms lvalue and rvalue are not something one runs into often in C/C++ programming, but when one does, it’s usually not immediately clear what they mean. The most common place to run into these terms are in compiler error & warning messages. For example, compiling the following with gcc: int foo() {return 2;} int main() { foo() = 2; return 0; } You get: test.c: In function 'main': test.c:8:5: error: lvalue required as left operand of assignment True, this code ...

   lvalue,rvalue,C++,locator value,elaboration     2011-12-15 07:51:38

  JavaScript to open link in new window without being popup blocked

To ensure security and reduce spamming, modern browsers have implemented very strict rules on when a new window can be opened in a web page. Currently browsers restrict that any new web page to be opened in a new window must be initiated with an user action. The action is usually an user click event. Otherwise, a popup blocker would show on the browser address bar which indicates that something is blocked. To workaround this issue, normally you should implement the window open logic in a click e...

   JAVASCRIPT,IFRAME,NEW WINDOW,OPEN LINK     2018-09-22 04:29:30

  Never create Ruby strings longer than 23 characters

Looking at things through a microscopesometimes leads to surprising discoveries Obviously this is an utterly preposterous statement: it’s hard to think of a more ridiculous and esoteric coding requirement. I can just imagine all sorts of amusing conversations with designers and business sponsors: “No… the size of this <input> field should be 23… 24 is just too long!” Or: “We need to explain to users that their subject lines should be les...

   Ruby,Specification,String,Interpreter,Optimization,23     2012-01-05 07:58:07

  HTML above flash (transparency + z-index)

We have faced this problem many of the times. When we want to display some message on top of all layers on a page or use some feature like jQuery light boxes. Normally the flash file continues to shine through the page. No matter what you do with layering the dom elements using z-index.See the layering flash content problem definition here.Before this, people used to dodge this issue with some fixes like hiding the flash area completely and then showing a static image of...

   HTML,Flash,Above,z-index,wmode,transpare     2011-05-01 15:46:34

  What are some lesser known but useful Unix commands?

A few that come to mind, some less known, some more: xargs or parallel: run things in parallel, with lots of options sed and awk: more well-known but still super useful for processing text files, and faster than Python or Ruby m4: simple macro processor screen: powerful terminal multiplexing and session persistence yes: print a string a lot cal: nice calendar env: run a command (useful in scripts) look: find English words (or lines in a file) beginning with a string cut and paste and join: data...

   Linux,Unix,Command,Less used     2011-12-27 09:27:49

  Don't Overload #nil?

There’s a popular post on Hacker News about writing confident code by, among other things, overloading Object#nil? and returning “null objects” instead of nil itself.DO NOT DO THIS.In Ruby, all objects (except nil itself) coerce to the boolean value true. Your object will be nil and true at the same time. Bad things will happen. Your coworkers will cry. Sad people from around the world will ask bewildering questions on your mailing list.Here’s what happen...

   Ruby,#nil,Overload,Object     2011-11-10 10:50:22

  CSS Tools: Reset CSS

The goal of a reset stylesheet is to reduce browser inconsistencies in things like default line heights, margins and font sizes of headings, and so on. The general reasoning behind this was discussed in a May 2007 post, if you're interested. Reset styles quite often appear in CSS frameworks, and the original "meyerweb reset" found its way into Blueprint, among others. The reset styles given here are intentionally very generic. There isn't any default color or background set for the bod...

   CSS,Cross browser compatibility,Reset,Partial reset     2011-12-05 02:44:11

  ConcurrentHashMap vs Collections.synchronizedMap()

ConcurrentHashMap and Collections.synchronizedMap() both provide thread-safe operations of collections of data. They are used in multithreaded programs to provide both thread safety and performance improvements. In many cases, we can use either of them. But the realization of thread safety is different for these two implementations. ConcurrentHashMap will create an HashEntry[] array internally to store the elements passed in from a Map, while Collections.synchronizedMap() will return a Synchroni...

   ConcurrentHashMap,Collections.synchronizedMap     2014-09-18 05:04:59

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