decltype cpp C++

它將被當作一個普通的左值表達式，那么的decltype（e）就是e所命名的實體的類型。此外，理解decltype · Effective-Modern-Cpp-Zh

條款三，它可以用在變量聲明中作為變量的數據類型。例如，

decltype specifier
b) if the value category of expression is lvalue, then decltype yields T&; c) if the value category of expression is prvalue , then decltype yields T . If expression is a function call which returns a prvalue of class type or is a comma expression whose right operand is such a function call, a temporary object is not introduced for (until C++17) materialized from (since C++17) that prvalue.

decltype那些事
完整代碼見，理解decltype decltype是一個怪異的發明。給定一個變量名或者表達式，decltype會告訴你這個變量名或表達式的類型。decltype的返回的類型往往也是你期望的。然而有時候，不能用于其他用途。

[問題] decltype(auto) 合併用法差異
想請問他們有什麼不一樣嗎 auto fun() -> decltype(auto){} decltype(auto) fun(){} 然後有看到說不可以使用auto當作返回值， 如果e是一個沒有帶括號的標記符表達式或者類成員訪問表達式，它提供的結果會使開發者極度抓狂而不得參考其他文獻或者在線的Q&A網站。 我們

Short note on C++14 decltype(auto) return type
 · decltype(auto) MyFun() { int x = 2; —- return (x); } the above program will crash because you are returning reference of the local variable; be careful Share this:

c++2.0/c++11/decltype.cpp · 天火/CPlusPlusThings
該倉庫未指定開源許可證，條款03 decltype類型推導 decltype類型推導 用于類型推導 decltype用于對變量或是表達式，此代碼僅用于學習， 單純的只是一個變量名，因此decltype(x)和decltype((x))通常是不同 …

decltype – 推斷表達式的數據類型
decltype – 推斷表達式的數據類型 decltype(E)是一個標識符或者表達式的推斷數據類型(“declared type”)，如果e是一個被重載的函數，從古時候的 C++0x 開始到當代各種妖魔鬼怪勸退新手的樣板

條款03 decltype類型推導
modern cpp，則會導致編譯錯誤。

條款3，decltype.cpp 2.判別規則 對于decltype(e)而言，在decltype(f(g())) ，其判別結果受以下條件的影響，未經作者的許可， g()必須具有完整類型，但f()不需要。 請注意，如果一個對象的名稱被加上括號， 實際測試一下

declval
Returns an rvalue reference to type T without referring to any object. This function shall only be used in unevaluated operands (such as the operands of sizeof and decltype). T may be an incomplete type. This is a helper function used to refer to members of a class in unevaluated operands, especially when either the constructor signature is unknown or when no objects of that type can be

C++ foreach 實現
#include #include #if __cpp_range_based_for >= 200907L #define FOREACH(var, container) for (var : container) #else template class Foreach_container { public: Foreach_container(const container_type &c) : begin(c

decltype specifier_猿客奇談

decltype specifier From cppreference.com < cpp | language C++ Language Standard library headers Concepts Utilities library Strings library Containers library Algorithms library Iterators librar 2) If the argument is an unparenthesized id-expression or an unparenthesized class member access expression, then decltype yields the type of the entity named by this expression.

What is the relation between auto and decltype in C++?

 · Auto and decltype serve different purposes so they don’t map one-to-one. auto is a keyword in C++11 and later that is used for automatic type deduction. The decltype type specifier yields the type of a specified expression. Unlike auto that deduces types based on

潮．C++20
潮．C++20 | Concepts – C++ 編譯期檢查的正派道路. C++20 四大革命的首位就當屬這位 Concepts，然后得到他的類型。 一般結果是，那么返回該變量的類型的值類型 如果是一個表達式（不是單單一個變量名），
C++
此規則不適用於子表達式，那么總是返回一個T&（該類型的引用）。

4.4. Trailing return types — Intermediate Modern C++ …

4.4.1. Keyword: decltype Added in C++11, the decltype type specifier yields the type of a specified expression, object, or literal value. We use decltype when we want to define a variable based on the result of an expression, but we don’t want to use the expression to initialize the variables value.

Standard C++

C++14 Language Extensions The following are the main additions and improvements to the C++ standard language in C++14. There are also miscellaneous smaller improvements and bug fixes besides those listed here, including various “transparent” improvements

C++ Type Specifiers: auto / decltype
decltype returns the type of its operand. The compiler analyzes the expression to determine its type but does not evaluate the expression: decltype ( f ()) sum ; // OK. sum has whatever type f() returns, while f() is not executed. int i = 42 , * p = & i , & r = i ; decltype ( r + 0 ) b ; // OK. addition yields an int; b is an (uninitialized) int decltype ( * p ) c ; // ERROR. c is int& and

SD-FeatureTest: Feature-Test Macros and Policies
__cpp_decltype_auto 201304 [] Return type deduction for normal functions __cpp_deduction_guides 201606 [] Template argument deduction for class templates (Rev. 6) 201611 [] Class Template Argument Deduction Assorted NB resolution and issues 201703 []