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Why doesn't the example compile, aka how does (co-, contra-, and in-) variance work?
...r. This declaration as a whole means that Function1 is contravariant in P and covariant in R. Thus, we can derive the following axioms:
T1' <: T1
T2 <: T2'
---------------------------------------- S-Fun
Function1[T1, T2] <: Function1[T1', T2']
Notice that T1' must be a subtype (or the ...
Find() vs. Where().FirstOrDefault()
I often see people using Where.FirstOrDefault() to do a search and grab the first element. Why not just use Find() ? Is there an advantage to the other? I couldn't tell a difference.
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How to convert a unix timestamp (seconds since epoch) to Ruby DateTime?
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DateTime.strptime can handle seconds since epoch. The number must be converted to a string:
require 'date'
DateTime.strptime("1318996912",'%s')
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采花大盗速成秘籍之YQL - 人工智能(AI) - 清泛IT论坛，有思想、有深度
采花大盗速成秘籍之YQL
理想情况下，在一个和谐的网络里，应该允许网站彼此自由的分享数据，不过和谐的网络就好像和谐的社会一样，从未真正存在过，除了少数开放了API的网站，更多的时候，我们只能通过采集来获得数据...
预编译头文件来自编译器的早期版本，或者预编译头为 C++ 而在 C 中使用它(...
现象&原因：
当 Visual C++ 项目启用了预编译头 (Precompiled header) 功能时，如果项目中同时混合有 .c 和 .cpp 源文件，则可能收到 C1853 编译器错误：fatal error C1853: 'pjtname.pch' precompiled header file is from a previous version of the compiler, or the...
Find the files that have been changed in last 24 hours
...ed in the last 24 hours (last full day) in a particular specific directory and its sub-directories:
find /directory_path -mtime -1 -ls
Should be to your liking
The - before 1 is important - it means anything changed one day or less ago.
A + before 1 would instead mean anything changed at least o...
Display current date and time without punctuation
For example, I want to display current date and time as the following format:
5 Answers
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What is that “total” in the very first line after ls -l? [closed]
...m does not mention that line, but info coreutils ls does. How comes man ls and info coreutils ls have different information about the same command? Why isn't ls just documented once? Having two different documentations for the same command seems like set up for failure.
– Hello...
Correct way to convert size in bytes to KB, MB, GB in JavaScript
... does not active her copied code anymore
Now, Fixed version unminified, and ES6'ed: (by community)
function formatBytes(bytes, decimals = 2) {
if (bytes === 0) return '0 Bytes';
const k = 1024;
const dm = decimals < 0 ? 0 : decimals;
const sizes = ['Bytes', 'KB', 'MB', 'GB', ...
What encoding/code page is cmd.exe using?
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Yes, it’s frustrating—sometimes type and other programs
print gibberish, and sometimes they do not.
First of all, Unicode characters will only display if the
current console font contains the characters. So use
a TrueType font like Lucida Console instead of the...