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Show pending migrations in rails
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This command will list all migrations with their status (UP or DOWN)
Rails 3 and 4
rake db:migrate:status
Rails 5
rake db:migrate:status
# Or
rails db:migrate:status
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How to specialize std::hash::operator() for user-defined type in unordered containers?
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You are expressly allowed and encouraged to add specializations to namespace std*. The correct (and basically only) way to add a hash function is this:
namespace std {
template <> struct hash<Foo>
{
size_t operator()(const...
HashSet vs LinkedHashSet
...ax(2*c.size(), 11), .75f, true); // <-- boolean dummy argument
addAll(c);
}
And (one example of) a HashSet constructor that takes a boolean argument is described, and looks like this:
/**
* Constructs a new, empty linked hash set. (This package private
* constructor is only used by Li...
Useless use of cat?
...my rationale.
I had not meant to be defensive in responding to him. After all, in my younger years, I would have written the command as grep foo file.txt | cut ... | cut ... because whenever you do the frequent single greps you learn the placement of the file argument and it is ready knowledge that...
What is the difference between an annotated and unannotated tag?
...you passed the -a flag for annotation and use the provided message.
Basically, it just amounts to whether you want the tag to have an annotation and some other information associated with it or not.
share
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Fastest way to count exact number of rows in a very large table?
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with (NOLOCK) is not something that allows it to run on production, and it can lead to an inaccurate count. When you use that hint, sure it prevents locks but the side effects on a production box are that you can count rows twice in some situations or skip rows...
Can I delete a git commit but keep the changes?
... back to the commit just before your current HEAD. However, it doesn't actually change the files in your working tree. As a result, the changes that were in that commit show up as modified - its like an 'uncommit' command. In fact, I have an alias to do just that.
git config --global alias.uncommit...
Length of an integer in Python
...ere are some benchmarks. The len(str()) is already behind for even quite small numbers
timeit math.log10(2**8)
1000000 loops, best of 3: 746 ns per loop
timeit len(str(2**8))
1000000 loops, best of 3: 1.1 µs per loop
timeit math.log10(2**100)
1000000 loops, best of 3: 775 ns per loop
timeit len...
Why switch is faster than if
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Because there are special bytecodes that allow efficient switch statement evaluation when there are a lot of cases.
If implemented with IF-statements you would have a check, a jump to the next clause, a check, a jump to the next clause and so on. With switch the JV...
Changing navigation bar color in Swift
I am using a Picker View to allow the user to choose the colour theme for the entire app.
30 Answers
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