constants

问题 I have a string, containing an Class name. It is, for example, a string containing "Article". That string came up from the params[]. What should I do to work with this string as if it was a class name? For instance, I want to do: Article.all and so on. Any idea? 回答1: This solution is better than eval as you are evaluating params hash that might be manipulated by the user and could contain harmful actions. As a general rule: Never evaluate user input directly, that's a big security hole. #

问题 ES6 onwards we have const . This is not allowed: const x; //declare first //and then initialize it if(condition) x = 5; else x = 10; This makes sense because it prevents us from using the constant before it's initialized. But if I do if(condition) const x = 5; else const x = 10; x becomes block scoped. So how to conditionally create a constant? 回答1: Your problem, as you know, is that a const has to be intialised in the same statement that it was declared in. This doesn't mean that the value

问题 In a Ruby on Rails application, where is the best place to define a constant? I have an array of constant data that I need available across all the controllers in my application. 回答1: Rails >= 3, the application is itself a module (living in config/application.rb ). You can store them in the application module module MyApplication SUPER_SECRET_TOKEN = "123456" end Then use MyApplication::SUPER_SECRET_TOKEN to reference the constant. Rails >= 2.1 && < 3 you should place them in /config

问题 I found out that Java supports constant folding of primitive types, but what about String s? Example If I create the following source code out.write("" + "<markup>" + "<nested>" + "Easier to read if it is split into multiple lines" + "</nested>" + "</markup>" + ""); What goes into the compiled code? Combined Version? out.write("<markup><nested>Easier to read if it is split into multiple lines</nested></markup>"); Or the less efficient run-time concatenation version? out.write(new

问题 I have an existing old project where only one base URL is defined statically in app constant class. Now I need to implement a spinner in login activity which have 3 spinner value and each value carry one base URL statically.So when user select value from spinner it will access base URL and logging accordingly.Now my question is can I change base URL programmatically in App constant class . so that i do not need to change entire code or make a setting class. 回答1: As per my understanding you

问题 In my MVC application I have many properties of DateTime datatype and I define DataFormatString on every new property in this datatype is defined as below: Model: [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)] public DateTime StartDate{ get; set; } [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)] public DateTime EndDate{ get; set; } Instead of this, I think there is another option to define these DataFormatStrings for just

问题 For our test scenarios - based on configuration of the application, we may want to either enable or disable a scenario. For this purpose, I created a custom IgnoreIfConfig Attribute like this : public class IgnoreIfConfigAttribute : Attribute, ITestAction { public IgnoreIfConfigAttribute(string config) { _config = config; } public void BeforeTest(ITest test) { if (_config != "Enabled") NUnit.Framework.Assert.Ignore("Test is Ignored due to Access level"); } public void AfterTest(ITest test) {

问题 In Doctrine you are provided with a Constant Variable that allows you to set a global Identifier column in all of the models that are generated by Doctrine's code. I am trying to figure out how I can override/shut off this value so that it does not create this column in a specific table. The Constant is: ATTR_DEFAULT_IDENTIFIER_OPTIONS It gets set in a bootstrapped PHP file and it automatically creates the appropriate table in your Database. Example Code: // set the default primary key to be

问题 In Doctrine you are provided with a Constant Variable that allows you to set a global Identifier column in all of the models that are generated by Doctrine's code. I am trying to figure out how I can override/shut off this value so that it does not create this column in a specific table. The Constant is: ATTR_DEFAULT_IDENTIFIER_OPTIONS It gets set in a bootstrapped PHP file and it automatically creates the appropriate table in your Database. Example Code: // set the default primary key to be

问题 Introduction Let's introduce this simple example: #include <cmath> class X { public: // Members /// A ^ B + A int A; /// A ^ B + B int B; public: // Specials X( const int & A, const int & B ) : A(A) , B(B) { const auto Pow = static_cast<int>(std::pow(A, B)); this->A += Pow; this->B += Pow; } }; Trivia Introduced class has two member variables: A and B . They take value of A ^ B + A and A ^ B + B , respectively. Both of them shares common complex initialization code (let's assume std::pow is