symbols

问题 It's well known to Rubyist & will call to_proc on a symbol, so [:a, :b, :c].map(&:to_s) is equivalent to [:a, :b, :c].map { |e| e.to_s } # => ["a", "b", "c"] Say I want to call another method right after to_s , these two implementations will work: [:a, :b, :c].map { |e| e.to_s.upcase } [:a, :b, :c].map(&:to_s).map(&:upcase) My question is, is there a way to chain the & Symbol#to_proc call in one parameter? Something like: [:a, :b, :c].map(&:to_s:upcase) Thanks! 回答1: If you're only doing: %i[a

问题 It was my impression that using #import would only import a file once per build, yet after trying to define a variable in a header, and then importing that header in two different source files, I get a duplicate symbol linker error for the variable. How is this possible? 回答1: #import makes header to be included once per file , but not per build. So your variable is defined in every file where you import your header and as global variable is visible by default in whole project you get linker

问题 This question already has an answer here : What is the “equals greater than” operator => in Ruby? (1 answer) Closed 5 years ago . While learning Ruby I've come across the "=>" operator on occasion. Usually I see it in the form of :symbol => value and it seems to be used frequently when passing values to functions. What exactly is that operator called? What does it do/mean? Is it built into Ruby or is it something that different frameworks like Rails and DataMapper add to the symbol class? Is

问题 Let's say I have a class called 'foo' in namespace "abc"... namespace abc { class foo { int a; int b; }; } ...and then say I have another class called "abc" in a different namespace #include "foo.h" namespace foo { class abc { abc::a = 10; }; } abc::a would not be a defined type, because it would be searching class abc, not namespace abc. How would I go about properlly referencing an object in another namespace, wherein that other namespace had the same name as the class I'm in? 回答1: You can

问题 The API documentation for the JavaScript functional programming library Ramda.js contains symbolic abbreviations but does not provide a legend for understanding these. Is there a place (website, article, cheatsheet, etc.) that I can go to to decipher these? Some examples from the Ramda.js API documentation: Number -> Number -> Number Apply f => f (a -> b) -> f a -> f b Number -> [a] -> [[a]] (*... -> a) -> [*] -> a {k: ((a, b, ..., m) -> v)} -> ((a, b, ..., m) -> {k: v}) Filterable f => (a ->

问题 What is the best way to create a Sympy equation, do something like take the derivative, and then plot the results of that equation? I have my symbolic equation, but can't figure out how to make an array of values for plotting. Here's my code: from sympy import symbols import matplotlib.pyplot as mpl t = symbols('t') x = 0.05*t + 0.2/((t - 5)**2 + 2) nums = [] for i in range(1000): nums.append(t) t += 0.02 plotted = [x for t in nums] mpl.plot(plotted) mpl.ylabel("Speed") mpl.show() In my case

问题 Scala has symbols - names that start with a single quote ' and which are a kind of string constants. I know symbols from Ruby (where they start with a colon). In Ruby they are used for some meta-programming tasks, like generating getters and setters for member variables (for example attr_reader :name to generate a getter for name ). I haven't seen a lot of use of symbols in Scala code yet. What are practical uses for symbols in Scala? 回答1: Do symbols really fit into Scala? In the wonderful

问题 I just starting Learn you a Haskell , and I saw this used in an example without explanation: tell :: (Show a) => [a] -> String What does this mean, in particular the => ? I know it won't work if I substitute -> or delete it, but I don't really understand why. 回答1: It's a constraint on the type, means a should be an instance of class Show . see for example here 回答2: Here's another way of looking at it. Some of a function's arguments are invisible, others are visible. A type input -> output

问题 I am trying define symbols a and b in following way a + 1 1 b 2 I am trying to do this by using define-symbol-macro (define-symbol-macro a '( ) (define-symbol-macro b ') ) but this way is not working. 回答1: What Lisp does with source code Common Lisp is an incredibly flexible language, in part because its source code can be easily represented using the same data structures that are used in the language. The most common form of macro expansion transforms the these structures into other

问题 Can someone please explain to me what the # symbol means in MS SQL Code. I've tried Googling it, and even searching on StackOverflow, but can't seem to find the answer. I feel like an idiot - having one of "those" days. Please help. 回答1: They normally prefix temporary tables. From the docs.... Prefix local temporary table names with single number sign (#table_name), and prefix global temporary table names with a double number sign (##table_name). 回答2: The pound sign # is used to prefix