language-construct | 易学教程

Is this special treatment of exit and die documented in PHP?

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问题 I've just read the page on Expressions in the PHP docs, and right at the top it says: The simplest yet most accurate way to define an expression is "anything that has a value". That simple definition includes all functions and most language constructs, however there a few language constructs that explicitly state they do not return a value. Here is a list of language constructs that do return a value: empty eval include include_once isset list require require_once print Here are the

Why would I use java.lang.Class.cast [duplicate]

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问题 This question already has answers here : When should I use the java 5 method cast of Class? (5 answers) Java Class.cast() vs. cast operator (8 answers) Closed 10 months ago . I recently stumbled upon a piece of code that went like this: Object o = .. ; Foo foo = Foo.class.cast(o); I was actually not even aware that java.lang.Class had a cast method, so I looked into the docs, and from what I gather this does simply do a cast to the class that the Class object represents. So the code above

Why does Scala support shadow variables? [closed]

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问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 8 years ago . I think that shadow variables are too dangerous to use them. Why does Scala support this language construct? There should be some

Is there a way to implement custom language features in C#?

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问题 I've been puzzling about this for a while and I've looked around a bit, unable to find any discussion about the subject. Lets assume I wanted to implement a trivial example, like a new looping construct: do..until Written very similarly to do..while do { //Things happen here } until (i == 15) This could be transformed into valid csharp by doing so: do { //Things happen here } while (!(i == 15)) This is obviously a simple example, but is there any way to add something of this nature? Ideally

Is there a way to implement custom language features in C#?

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Is there a way to implement custom language features in C#?

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What does this syntax ( page = $page ? $page : 'default' ) in PHP mean?

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问题 I'm new to PHP. I came across this syntax in WordPress. What does the last line of that code do? $page = $_SERVER['REQUEST_URI']; $page = str_replace("/","",$page); $page = str_replace(".php","",$page); $page = $page ? $page : 'default' 回答1: It's an example of the conditional operator in PHP. It's the shorthand version of: if (something is true ) { Do this } else { Do that } See Using If/Else Ternary Operators http://php.net/manual/en/language.operators.comparison.php . 回答2: That's the

How can I use C# style enumerations in Ruby?

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问题 I just want to know the best way to emulate a C# style enumeration in Ruby. 回答1: Specifically, I would like to be able to perform logical tests against the set of values given some variable. Example would be the state of a window: "minimized, maximized, closed, open" If you need the enumerations to map to values (eg, you need minimized to equal 0, maximised to equal 100, etc) I'd use a hash of symbols to values, like this: WINDOW_STATES = { :minimized => 0, :maximized => 100 }.freeze The

Python: Any way to declare constant parameters?

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问题 I have a method: def foo(bar): # ... Is there a way to mark bar as constant? Such as "The value in bar cannot change" or "The object pointed to by bar cannot change". 回答1: If bar is an inmutable object, bar won't change during the function. You can also create your own constant object. The recipe here. 回答2: No. What's the point? If you're writing the function, isn't it up to you to make sure bar doesn't change? Or if you're calling the function, who cares? 来源： https://stackoverflow.com

How can I use C# style enumerations in Ruby?

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I just want to know the best way to emulate a C# style enumeration in Ruby. Specifically, I would like to be able to perform logical tests against the set of values given some variable. Example would be the state of a window: "minimized, maximized, closed, open" If you need the enumerations to map to values (eg, you need minimized to equal 0, maximised to equal 100, etc) I'd use a hash of symbols to values, like this: WINDOW_STATES = { :minimized => 0, :maximized => 100 }.freeze The freeze (like nate says) stops you from breaking things in future by accident. You can check if something is