Menu
Here is what I want to do:
template <typename T> void f(DisableDeduction<T> obj) {std::cout << obj;}
// Here DisableDeduction<T> aliases T, but in a such way
// that would prevent compiler from deducing T based
// on provided argument.
/* ... */
f<int>(1); // Works.
f(1); // Error, can't deduce template parameter based on argument.
This is how I currently achieve it:
template <typename T> struct DisableDeduction_Internal {using type = T;};
template <typename T> using DisableDeduction = typename DisableDeduction_Internal<T>::type;
It works perfectly (as described), but it introduces one extra helper type.
But can I achieve same result without extra types?
514
Template argument deduction is used when selecting user-defined conversion function template arguments. A is the type that is required as the result of the conversion. P is the return type of the conversion function template.
There are ways to restrict the types you can use inside a template you write by using specific typedefs inside your template. This will ensure that the compilation of the template specialisation for a type that does not include that particular typedef will fail, so you can selectively support/not support certain types.
Class Template Argument Deduction (CTAD) is a C++17 Core Language feature that reduces code verbosity. C++17's Standard Library also supports CTAD, so after upgrading your toolset, you can take advantage of this new feature when using STL types like std::pair and std::vector.
A non-type template argument provided within a template argument list is an expression whose value can be determined at compile time. Such arguments must be constant expressions, addresses of functions or objects with external linkage, or addresses of static class members.
You can do it by putting T in non deducible context (to the left of ::), and use std::common_type from <type_traits>.
example:
template <typename T> void f(typename std::common_type<T>::type obj) {std::cout << obj;}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
