Template argument deduction is a compiler attempt to deduce template arguments when some are omitted.
Questions tagged [template-argument-deduction]
692 questions
13
votes
2 answers
Why is template argument deduction failing for pointer-to-member-function?
With g++ 5.4, this
struct B {
void f() {}
};
struct D : public B {
void g() {}
};
template
void foo(void (T::*)(), void (T::*)())
{}
int main()
{
foo(&D::f, &D::g);
}
fails due to "deduced conflicting types for parameter…
fizzer
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13
votes
2 answers
Nested template argument deduction for class templates not working
In this Q&A I wrote a little wrapper class that provides reverse iterator access to a range, relying on the c++1z language feature template argument deduction for class templates (p0091r3, p0512r0)
#include
#include
#include…
TemplateRex
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13
votes
3 answers
Deduce template argument from std::function call signature
Consider this template function:
template
ReturnT foo(const std::function& fun)
{
return fun();
}
Why isn't it possible for the compiler to deduce ReturnT from the passed call signature?
bool bar() { /* ... */…
Karl von Moor
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12
votes
1 answer
Should the order of template arguments matter when they are all deduced?
I'm getting a discrepancy between Clang, GCC and MSVC, where GCC and Clang do what I expect:
#include
template //< Bad
//template //< OK
//template…
Ben
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12
votes
2 answers
Partial class template argument deduction in C++17
In the example below, we use the C++17 feature "Class template argument deduction" to deduce that val is of type Base:
template
struct Base {
Base(T, U) { };
Base(T, U, V) { };
Base(V) {…
Phil-ZXX
- 2,359
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12
votes
1 answer
Function template overload resolution with two parameter packs
Consider the following code:
#include
template
int f(T...) { return 1; }
template
int f(T...) { return 2; }
int main()
{
std::cout << f(1);
}
It compiles and prints 1 on gcc 8.2, but fails to…
user10605163
12
votes
1 answer
g++ and clang++ different behaviour with pointer to variadic template functions
Another "who's right between g++ and clang++ ?" question for C++ standard gurus.
The code is the following
template
struct bar
{ };
template
void foo (bar const &)
{ }
int main ()
{
foo(bar
max66
- 65,235
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12
votes
1 answer
Are user defined deduction guides involving template template parameter as a template for guidance standard compliant
Background
Yesterday I asked a question about the guarantees of deduction guides usage in case of template template parameters. I was really surprised when Barry changed his answer to the confirmation of standard complianceness of the code. My…
W.F.
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12
votes
2 answers
SFINAE and the address of an overloaded function
I'm experimenting with resolving the address of an overloaded function (bar) in the context of another function's parameter (foo1/foo2).
struct Baz {};
int bar() { return 0; }
float bar(int) { return 0.0f; }
void bar(Baz *) {}
void foo1(void…
Quentin
- 62,093
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12
votes
5 answers
Can't deduce template type
I'm trying to pass an iterator as a template parameter to a template method, but the compiler complains that:
error C2783: 'void Test::Assert(std::vector::const_iterator)':
could not deduce template argument for 'T'
The code that produces the…
Q-bertsuit
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12
votes
1 answer
What's the point of "boost::mpl::identity::type" here?
I was checking the implementation of clamp in boost:
template
T const & clamp ( T const& val,
typename boost::mpl::identity::type const & lo,
typename boost::mpl::identity::type const & hi, Pred p )
…
Karoly Horvath
- 94,607
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12
votes
1 answer
Mixing variadic template values and variadic deduced types
Is the following perfectly defined by the standard ?
#include
template
void f(Types&&... values)
{
std::cout<
Vincent
- 57,703
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- 388
11
votes
2 answers
Template argument deduction for an argument of a function type
Consider the following program.
#include
template
void f( void ( *fn )( T ) )
{
fn( 42 );
}
void g( int x )
{
std::cout << "g( " << x << " );\n";
}
int main()
{
f( g );
}
The program compiles successfully and…
Vlad from Moscow
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11
votes
2 answers
Is it possible for the template parameter to be a reference type?
I have started to learn C++ and currently I am trying to get started with templates, so please bear with me, if my wording is not 100% accurate.
I am using the following literature:
C++ Templates: The Complete Guide (2nd Edition)
Effective Modern…
polygamma
- 113
- 6
11
votes
5 answers
Array class that will accept an braced-init-list and deduce length
This has been asked before, but I'm curious to see if anything has changed in newer C++ standards. Any current or future standard is acceptable.
Q: Is there anyway to create an Array class that can be initialized with a braced-init-list without…
Adam
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