constants

问题 So Im creating this Event Tracker app and I have two screens which are the map and the events list. I am trying to get the place list to be equal to my places in my App state. Bare in mind that placeList is a modifiable list that I need to add places to this list. However I am getting a "The default value of an optional parameter must be constant" whenever I initialize this.places=PlaceMapState.placeList and I cant change it to a constant since i need it to update my list of places in the

问题 So Im creating this Event Tracker app and I have two screens which are the map and the events list. I am trying to get the place list to be equal to my places in my App state. Bare in mind that placeList is a modifiable list that I need to add places to this list. However I am getting a "The default value of an optional parameter must be constant" whenever I initialize this.places=PlaceMapState.placeList and I cant change it to a constant since i need it to update my list of places in the

问题 This question already has an answer here : When are const volatile objects necessary? (1 answer) Closed 4 years ago . Say I have some object declared as const volatile : According to the C++ standard ($7.1.5.1/8): [..] volatile is a hint to the implementation to avoid aggressive optimization involving the object because the value of the object might be changed by means undetectable by an implementation.[...] However, the const qualifier implies than the object is not subject to change, so the

问题 This question already has an answer here : When are const volatile objects necessary? (1 answer) Closed 4 years ago . Say I have some object declared as const volatile : According to the C++ standard ($7.1.5.1/8): [..] volatile is a hint to the implementation to avoid aggressive optimization involving the object because the value of the object might be changed by means undetectable by an implementation.[...] However, the const qualifier implies than the object is not subject to change, so the

问题 Given this Google Apps Script script: 'use strict' const foo = 2; function bar() { Logger.log(foo + 2); } Running the function bar results in a TypeError: redeclaration of const foo. Why? How is foo being redeclared? 回答1: Seems like it's due to spotty implementation of ES6. I still get the error if I remove foo from the function, so the error is coming from the global const declaration. The below code produces the same error, but no error if you comment out const foo. const foo = 2; function

问题 Given this Google Apps Script script: 'use strict' const foo = 2; function bar() { Logger.log(foo + 2); } Running the function bar results in a TypeError: redeclaration of const foo. Why? How is foo being redeclared? 回答1: Seems like it's due to spotty implementation of ES6. I still get the error if I remove foo from the function, so the error is coming from the global const declaration. The below code produces the same error, but no error if you comment out const foo. const foo = 2; function

问题 When reading tutorials and code written in C++, I often stumble over the const keyword. I see that it is used like the following: const int x = 5; I know that this means that x is a constant variable and probably stored in read-only memory. But what are void myfunc( const char x ); and int myfunc( ) const; ? 回答1: void myfunc(const char x); This means that the parameter x is a char whose value cannot be changed inside the function. For example: void myfunc(const char x) { char y = x; // OK x =

问题 When reading tutorials and code written in C++, I often stumble over the const keyword. I see that it is used like the following: const int x = 5; I know that this means that x is a constant variable and probably stored in read-only memory. But what are void myfunc( const char x ); and int myfunc( ) const; ? 回答1: void myfunc(const char x); This means that the parameter x is a char whose value cannot be changed inside the function. For example: void myfunc(const char x) { char y = x; // OK x =

问题 I get the following error in Eclipse when trying to compile (c++) ../CardDeck.cpp:17:22: error: passing ‘const CardDeck’ as ‘this’ argument of ‘int CardDeck::size()’ discards qualifiers [-fpermissive] if I change int size() method to int size() const the error msg is gone and its compiled. I dont know why ? the .H file is the following : #include "Card.h" #include <vector> using namespace std; class CardDeck{ private: vector<Card*> deck; public: int size(); CardDeck(); CardDeck(const CardDeck

问题 I get the following error in Eclipse when trying to compile (c++) ../CardDeck.cpp:17:22: error: passing ‘const CardDeck’ as ‘this’ argument of ‘int CardDeck::size()’ discards qualifiers [-fpermissive] if I change int size() method to int size() const the error msg is gone and its compiled. I dont know why ? the .H file is the following : #include "Card.h" #include <vector> using namespace std; class CardDeck{ private: vector<Card*> deck; public: int size(); CardDeck(); CardDeck(const CardDeck