Apart from the apparent difference of having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen. const‘s are implicitly static. You use a ClassName.ConstantName notation to access them. There is … Read more
public static readonly fields are a little unusual; public static properties (with only a get) would be more common (perhaps backed by a private static readonly field). const values are burned directly into the call-site; this is double edged: it is useless if the value is fetched at runtime, perhaps from config if you change … Read more
Basic meaning and syntax Both keywords can be used in the declaration of objects as well as functions. The basic difference when applied to objects is this: const declares an object as constant. This implies a guarantee that once initialized, the value of that object won’t change, and the compiler can make use of this … Read more
Use of ‘const’ for function parameters
The difference is that const char * is a pointer to a const char, while char * const is a constant pointer to a char. The first, the value being pointed to can’t be changed but the pointer can be. The second, the value being pointed at can change but the pointer can’t (similar to … Read more
EL 3.0 or newer If you’re already on Java EE 7 / EL 3.0, then the @page import will also import class constants in EL scope. <%@ page import=”com.example.YourConstants” %> This will under the covers be imported via ImportHandler#importClass() and be available as ${YourConstants.FOO}. Note that all java.lang.* classes are already implicitly imported and available … Read more
For a detailed explanation, please see the heading “Avoid Duplication in const and Non-const Member Function,” on p. 23, in Item 3 “Use const whenever possible,” in Effective C++, 3d ed by Scott Meyers, ISBN-13: 9780321334879. Here’s Meyers’ solution (simplified): struct C { const char & get() const { return c; } char & get() … Read more
It used to be generally recommended best practice1 to use pass by const ref for all types, except for builtin types (char, int, double, etc.), for iterators and for function objects (lambdas, classes deriving from std::*_function). This was especially true before the existence of move semantics. The reason is simple: if you passed by value, … Read more
You should create a header file like: // Constants.h FOUNDATION_EXPORT NSString *const MyFirstConstant; FOUNDATION_EXPORT NSString *const MySecondConstant; //etc. (You can use extern instead of FOUNDATION_EXPORT if your code will not be used in mixed C/C++ environments or on other platforms.) You can include this file in each file that uses the constants or in the … Read more
In C the type of a string literal is a char[] – it’s not const according to the type, but it is undefined behavior to modify the contents. Also, 2 different string literals that have the same content (or enough of the same content) might or might not share the same array elements. From the … Read more