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做了个购物清单App后，我才真正搞懂App Inventor 2的变量 - App应用开发 - ...
...局部变量"遮蔽"。
解法：全局变量统一加前缀 g_（如 g_count），或用描述性名称（如 totalItemCount）。
坑3：初始化顺序
在 Screen.Initialize 里先用了变量，再初始化它。变量还没创建就被读取，返回空值。
解法：所有...
Update just one gem with bundler
...bundle update
> ruby -v
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin19]
> gem -v
3.0.3
> bundle -v
Bundler version 2.1.4
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Generating random integer from a range
...uch better ways of getting something that is uniformly distributed and actually random.
– Mgetz
Sep 12 '13 at 19:14
1
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What are some compelling use cases for dependent method types?
...argkeys: Tuple[DependentHashKey,DependentHashKey])(func: Env => argkeys._0.ValueType => argkeys._1.ValueType => A): A. We wouldn't use a collection of argument keys, because the element types would be subsumed (unknown at compile-time) in the type of collection.
– Shel...
Increasing the maximum number of TCP/IP connections in Linux
...local_port_range = 32768 61000
net.ipv4.tcp_fin_timeout = 60
This basically means your system cannot consistently guarantee more than (61000 - 32768) / 60 = 470 sockets per second. If you are not happy with that, you could begin with increasing the port_range. Setting the range to 15000 61000 is...
MySQL: Transactions vs Locking Tables
...is transferred. And the bank's account, into which they'll happily deposit all the service fees charged on the transaction. Given (as everyone knows these days) that banks are extraordinarily stupid, let's say their system works like this:
$balance = "GET BALANCE FROM your ACCOUNT";
if ($balance &l...
Opposite of %in%: exclude rows with values specified in a vector
... use
`%not in%` <- function (x, table) is.na(match(x, table, nomatch=NA_integer_))
Another way is:
function (x, table) match(x, table, nomatch = 0L) == 0L
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How to change the output color of echo in Linux
... comment, if you are using the echo command, be sure to use the -e flag to allow backslash escapes.
# Continued from above example
echo -e "I ${RED}love${NC} Stack Overflow"
(don't add "\n" when using echo unless you want to add additional empty line)
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How do I make an http request using cookies on Android?
...ookies when I make subsequent requests). It'd be nice to preserve any and all cookies, but really the only one I care about is the session cookie.
...
switch / pattern matching idea
... and some very smart people have done some very cool things in C#, but actually using it feels heavy.
What I have ended up using often (across-projects) in C#:
Sequence functions, via extension methods for IEnumerable. Things like ForEach or Process ("Apply"? -- do an action on a sequence item as...