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When and why are database joins expensive?
...ires retrieval of only the keys. In practice, not even the key values are fetched: the key hash values are used for join comparisons, mitigating the cost of multi-column joins and radically reducing the cost of joins involving string comparisons. Not only will vastly more fit in cache, there's a lot...
Simple way to encode a string according to a password?
...rs from the lower ascii range! See precedence of % operator, unicode input etc. See qneill's answer for working code
– le_m
Nov 14 '14 at 23:23
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What is an existential type?
...definition, list all possible uses, their relation to abstract data types, etc.) because I'm simply not knowledgeable enough for that. I'll demonstrate only (using Java) what this HaskellWiki article states to be the principal effect of existential types:
Existential types can be used for severa...
What is the optimal algorithm for the game 2048?
...ontaining no hard-coded intelligence (i.e no heuristics, scoring functions etc). The AI should "know" only the game rules, and "figure out" the game play. This is in contrast to most AIs (like the ones in this thread) where the game play is essentially brute force steered by a scoring function repre...
What is a NullPointerException, and how do I fix it?
...ou should know, Java types are divided into primitive types (boolean, int, etc.) and reference types. Reference types in Java allow you to use the special value null which is the Java way of saying "no object".
A NullPointerException is thrown at runtime whenever your program attempts to use a null...
How can I sort arrays and data in PHP?
...ilar. Your rewrite contains a lot of details (pass by reference, big table etc.), but that detail distracts from the smooth introduction to the core topic of the workings of the comparison function, IMHO. I explicitly refer to the manual several times on purpose, because that's where such detail sho...
What Every Programmer Should Know About Memory?
...spend the time reading the manuals about details about the actual timings, etc. But for people interested in the HW low level stuff? Maybe not useful, but at least entertaining.
– Voo
Nov 14 '11 at 18:52
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What kinds of patterns could I enforce on the code to make it easier to translate to another program
...plication of translation rules, regeneration of source text with comments, etc., all parameterized by explicit definitions of computer languages.
The amount of machinery you need to do this well is vast (especially if you want to be able to do this for multiple languages in a general way), and then...
Is quitting an application frowned upon?
... being
PUSHed to the device, lists with tasks
that always should be there, etc.).
I don't know what "lists with tasks that always should be there" means, but the "data being PUSHed to the device" is a pleasant fiction and should not be done by activity in any case. Use a scheduled task (via AlarmMa...
DDD - the rule that Entities can't access Repositories directly
... and specifications and so on), right? But if none of them are allowed to fetch data via Repositories, how am I supposed to write any (reasonably complicated) business logic? For example: Chatroom user is not allowed to change their name to a name thats already been used by someone else. I'd like th...