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Create singleton using GCD's dispatch_once in Objective-C
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This is a perfectly acceptable and thread-safe way to create an instance of your class. It may not technically be a "singleton" (in that there can only ever be 1 of these objects), but as long as you only use the [Foo sharedFoo] method to access the objec...
What are good examples of genetic algorithms/genetic programming solutions? [closed]
Genetic algorithms (GA) and genetic programming (GP) are interesting areas of research.
34 Answers
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Adding a column to an existing table in a Rails migration
...ontaining line:
add_column :users, email, string
Then do a rake db:migrate and it'll run the new migration, creating the new column.
If you have not yet run the original migration you can just edit it, like you're trying to do. Your migration code is almost perfect: you just need to remove the add_...
Remove a string from the beginning of a string
...str($str, strlen($prefix));
}
Takes: 0.0369 ms (0.000,036,954 seconds)
And with:
$prefix = 'bla_';
$str = 'bla_string_bla_bla_bla';
$str = preg_replace('/^' . preg_quote($prefix, '/') . '/', '', $str);
Takes: 0.1749 ms (0.000,174,999 seconds) the 1st run (compiling), and 0.0510 ms (0.000,051,...
What should I do if two libraries provide a function with the same name generating a conflict?
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If you control one or both: edit one to change the name and recompile Or equivalently see Ben and unknown's answers which will work without access to the source code.
If you don't control either of them you can wrap one of them up. That is compile another (statically linked!) libr...
In which order do CSS stylesheets override?
... more general ones. Specificity is defined based on how many IDs, classes, and element names are involved, as well as whether the !important declaration was used. When multiple rules of the same "specificity level" exist, whichever one appears last wins.
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How can I get the full/absolute URL (with domain) in Django?
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Use handy request.build_absolute_uri() method on request, pass it the relative url and it'll give you full one.
By default, the absolute URL for request.get_full_path() is returned, but you can pass it a relative URL as the first...
Binary Data in MySQL [closed]
...a BLOB data type / attribute domain. BLOB is short for Binary Large Object and that column data type is specific for handling binary data.
See the relevant manual page for MySQL.
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What is the C# Using block and why should I use it? [duplicate]
...eDisposableType()) {
OperateOnType(u);
}
The second is easier to read and maintain.
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How do I log errors and warnings into a file?
How do I turn on all error and warnings and log them to a file, but to set up all of that within the script (not changing anything in php.ini)?
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