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Why does Clojure have “keywords” in addition to “symbols”?
...u can use a double-colon to make a namespace-qualified keyword.
user> :foo
:foo
user> ::foo
:user/foo
Common Lisp has keywords, as do Ruby and other languages. They are slightly different in those languages of course. Some differences between Common Lisp keywords and Clojure keywords:
K...
How to sort git tags by version string order of form rc-X.Y.Z.W?
...
Prepend "-" to reverse sort order.
So, if you have:
git tag foo1.3 &&
git tag foo1.6 &&
git tag foo1.10
Here is what you would get:
# lexical sort
git tag -l --sort=refname "foo*"
foo1.10
foo1.3
foo1.6
# version sort
git tag -l --sort=version:refname "foo*"
foo1.3
...
What is the difference between ${var}, “$var”, and “${var}” in the Bash shell?
...races ($var vs. ${var})
In most cases, $var and ${var} are the same:
var=foo
echo $var
# foo
echo ${var}
# foo
The braces are only needed to resolve ambiguity in expressions:
var=foo
echo $varbar
# Prints nothing because there is no variable 'varbar'
echo ${var}bar
# foobar
Quotes ($var vs. "...
What is the Python equivalent of static variables inside a function?
...
A bit reversed, but this should work:
def foo():
foo.counter += 1
print "Counter is %d" % foo.counter
foo.counter = 0
If you want the counter initialization code at the top instead of the bottom, you can create a decorator:
def static_vars(**kwargs):
d...
Split data frame string column into multiple columns
...ry(tidyr)
before <- data.frame(
attr = c(1, 30 ,4 ,6 ),
type = c('foo_and_bar', 'foo_and_bar_2')
)
before %>%
separate(type, c("foo", "bar"), "_and_")
## attr foo bar
## 1 1 foo bar
## 2 30 foo bar_2
## 3 4 foo bar
## 4 6 foo bar_2
...
Python Remove last 3 characters of a string
...
Removing any and all whitespace:
foo = ''.join(foo.split())
Removing last three characters:
foo = foo[:-3]
Converting to capital letters:
foo = foo.upper()
All of that code in one line:
foo = ''.join(foo.split())[:-3].upper()
...
Reference: What is variable scope, which variables are accessible from where and what are “undefined
...cope", or "places from which they are accessible". Just because you wrote $foo = 'bar'; once somewhere in your application doesn't mean you can refer to $foo from everywhere else inside the application. The variable $foo has a certain scope within which it is valid and only code in the same scope ha...
When is a C++ destructor called?
...s out of scope,
// but not the object it pointed to. memory leak
if (1) {
Foo *myfoo = new Foo("foo");
}
// pointer is destroyed because it goes out of scope,
// object it points to is deleted. no memory leak
if(1) {
Foo *myfoo = new Foo("foo");
delete myfoo;
}
// no memory leak, object goes o...
Struct Constructor in C++?
...r problems.
If you declare your struct like this:
typedef struct{
int x;
foo(){};
} foo;
You will have problems trying to declare a constructor. This is of course because you haven't actually declared a struct named "foo", you've created an anonymous struct and assigned it the alias "foo". Thi...
Call a “local” function within module.exports from another function in module.exports?
...
Change this.foo() to module.exports.foo()
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