Chapter 1. Deducing Types Flashcards
Item 1: Understand template type deduction.
During template type deduction, arguments that are references are treated as non-references, i.e., their reference-ness is ignored.
When deducing types for universal reference parameters, lvalue arguments get special treatment.
When deducing types for by-value parameters, const and/or volatile arguments are treated as non-const and non-volatile.
During template type deduction, arguments that are array or function names decay to pointers, unless they’re used to initialize references.
Item 2: Understand auto type deduction.
auto type deduction is usually the same as template type deduction, but auto type deduction assumes that a braced initializer represents a std::initializer_list, and template type deduction doesn’t.
auto in a function return type or a lambda parameter implies template type deduction, not auto type deduction.
Item 3: Understand decltype.
decltype almost always yields the type of a variable or expression without any modifications.
For lvalue expressions of type T other than names, decltype always reports a type of T&.
C++14 supports decltype(auto), which, like auto, deduces a type from its initializer, but it performs the type deduction using the decltype rules.
Item 4: Know how to view deduced types.
Deduced types can often be seen using IDE editors, compiler error messages, and the Boost TypeIndex library.
The results of some tools may be neither helpful nor accurate, so an understanding of C++’s type deduction rules remains essential.
