The C++ detection idiom a programming pattern for detecting valid usages of types. It was introduced in WG21 document N4436 and will be part of the C++17 standard library.
A full description of the idiom can be found in WG21 N4436.
Questions tagged [detection-idiom]
8 questions
5
votes
0 answers
Detecting whether or not a callable object is binary (including generic constrained lambdas)
I'm trying to detect whether or not a callable object is binary (i.e. if its operator() takes two arguments). I want to perform this check on lambdas, including generic lambdas and constrained generic lambdas (e.g. with trailing std::enable_if_t…
Vittorio Romeo
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4
votes
3 answers
Counting arguments of an arbitrary callable with the C++ detection idiom
I've been using the C++ detection idiom create a metafunction for determining the number of arguments to an arbitrary callable. So far, I have this (full, compilable code at http://ideone.com/BcgDhv):
static constexpr auto max_num_args =…
Daisy Sophia Hollman
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3
votes
0 answers
Is possible to write a trait to detect a friend class declaration?
I would like to know if it is possible to write a trait capable to detect a friend class declaration. I'm particularly interested in the case of forward declaration, like so:
struct Baz
{
friend struct Foo;
};
struct Foo {};
Please no Boost or…
Antonio Cantarella
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2
votes
0 answers
why does type_identity break the implementation of is_detected
p0887r1:
2.3 Fundamental metafunction building block
There are two ubiquitous idioms for type traits:
define a public data member value with a given value
define a public member typedef type that names a given type
It is surprising that there is…
Chen Li
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1
vote
1 answer
SFINAE to detect operation when it is forbidden to call with temporary
It is possible to use the following pattern to detect whether or not x can be applied to T
template
struct CanDoX: std::false_type{};
template
struct CanDoX
user877329
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0
votes
0 answers
Emulating template constraints in C++14
I'm coding in C++14 a program that uses template classes and functions. I don't like the compiler error messages I get when the template types don't fulfill the requirements I ask for with std::enable_if
I wondered if I could do better trying to…
Rodrigo Torres
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votes
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Problem with using OnIdiom on VS for Mac using Xamarin Forms
I have always used this the same way and it always worked. After an update I keep getting an error. Can someone help me out?
This is the error I get.
Mitchell Rodrigues
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0
votes
2 answers
OnIdiom for Grid columnspan
I need to use OnIdiom for grid column definition, but it isn't working. See my code below. Can anyone tell me what I am doing wrong and suggest a solution?
…
Riyas
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