Clang fails to initialize static const template member
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In order to force the execution of a template method at program start one can initialize a static member with a static method. Then the method is run at program start for every instantiation of the template class:
#include <cstdio>
template<typename t, t value>
struct dummy_user_t {};
template<int i>
struct my_struct_t
{
static int s_value;
// "use" s_value so it's initialized
using value_user_t = dummy_user_t<const int&, s_value>;
static int method()
{
printf("Hello %i!n", i);
return 0;
}
};
// initialize s_value with method() to run it at program start
template<int i>
int my_struct_t<i>::s_value {my_struct_t<i>::method()};
// instantiate my_struct_t
template struct my_struct_t<6>;
int main()
{
// nothing here
}
The output will be Hello 6!
This code compiles on all three major compilers but when you make s_value const it won't work in clang anymore (3.4 - 7.0) while still working in MSVC and GCC:
<source>:19:52: error: no member 'method' in 'my_struct_t<6>'; it has not yet been instantiated
const int my_struct_t<i>::s_value {my_struct_t<i>::method()};
^
<source>:10:51: note: in instantiation of static data member 'my_struct_t<6>::s_value' requested here
using value_user_t = dummy_user_t<const int&, s_value>;
^
<source>:21:17: note: in instantiation of template class 'my_struct_t<6>' requested here
template struct my_struct_t<6>;
^
<source>:11:16: note: not-yet-instantiated member is declared here
static int method()
^
1 error generated.
Try it out yourself:
With non const int: https://godbolt.org/z/m90bgS
With const int: https://godbolt.org/z/D3ywDq
What do you think? Is there any reason clang is rejecting this or is it a bug?
c++ clang compiler-bug
asked Nov 15 at 18:25
HenrikS
148110
|
show 3 more comments
up vote
1
down vote
favorite
In order to force the execution of a template method at program start one can initialize a static member with a static method. Then the method is run at program start for every instantiation of the template class:
#include <cstdio>
template<typename t, t value>
struct dummy_user_t {};
template<int i>
struct my_struct_t
{
static int s_value;
// "use" s_value so it's initialized
using value_user_t = dummy_user_t<const int&, s_value>;
static int method()
{
printf("Hello %i!n", i);
return 0;
}
};
// initialize s_value with method() to run it at program start
template<int i>
int my_struct_t<i>::s_value {my_struct_t<i>::method()};
// instantiate my_struct_t
template struct my_struct_t<6>;
int main()
{
// nothing here
}
The output will be Hello 6!
This code compiles on all three major compilers but when you make s_value const it won't work in clang anymore (3.4 - 7.0) while still working in MSVC and GCC:
<source>:19:52: error: no member 'method' in 'my_struct_t<6>'; it has not yet been instantiated
const int my_struct_t<i>::s_value {my_struct_t<i>::method()};
^
<source>:10:51: note: in instantiation of static data member 'my_struct_t<6>::s_value' requested here
using value_user_t = dummy_user_t<const int&, s_value>;
^
<source>:21:17: note: in instantiation of template class 'my_struct_t<6>' requested here
template struct my_struct_t<6>;
^
<source>:11:16: note: not-yet-instantiated member is declared here
static int method()
^
1 error generated.
Try it out yourself:
With non const int: https://godbolt.org/z/m90bgS
With const int: https://godbolt.org/z/D3ywDq
What do you think? Is there any reason clang is rejecting this or is it a bug?
c++ clang compiler-bug
asked Nov 15 at 18:25
HenrikS
148110
Move the explicit instantiation above the usage ofmy_struct_t<i>::method()andclangcompiles like a champ: godbolt.org/z/758iFF
– Swordfish
Nov 15 at 18:30
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
Another fix would be to move the type alias declaration beneath the definition ofmy_struct_t<i>::method().
– Swordfish
Nov 15 at 19:35
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Please re-read my last comment. You can have yourint constwithclangif you moveusing value_user_t = dummy_user_t<const int&, s_value>;to after the definition ofmethod().
– Swordfish
Nov 15 at 19:38
|
show 3 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
In order to force the execution of a template method at program start one can initialize a static member with a static method. Then the method is run at program start for every instantiation of the template class:
#include <cstdio>
template<typename t, t value>
struct dummy_user_t {};
template<int i>
struct my_struct_t
{
static int s_value;
// "use" s_value so it's initialized
using value_user_t = dummy_user_t<const int&, s_value>;
static int method()
{
printf("Hello %i!n", i);
return 0;
}
};
// initialize s_value with method() to run it at program start
template<int i>
int my_struct_t<i>::s_value {my_struct_t<i>::method()};
// instantiate my_struct_t
template struct my_struct_t<6>;
int main()
{
// nothing here
}
The output will be Hello 6!
This code compiles on all three major compilers but when you make s_value const it won't work in clang anymore (3.4 - 7.0) while still working in MSVC and GCC:
<source>:19:52: error: no member 'method' in 'my_struct_t<6>'; it has not yet been instantiated
const int my_struct_t<i>::s_value {my_struct_t<i>::method()};
^
<source>:10:51: note: in instantiation of static data member 'my_struct_t<6>::s_value' requested here
using value_user_t = dummy_user_t<const int&, s_value>;
^
<source>:21:17: note: in instantiation of template class 'my_struct_t<6>' requested here
template struct my_struct_t<6>;
^
<source>:11:16: note: not-yet-instantiated member is declared here
static int method()
^
1 error generated.
Try it out yourself:
With non const int: https://godbolt.org/z/m90bgS
With const int: https://godbolt.org/z/D3ywDq
What do you think? Is there any reason clang is rejecting this or is it a bug?
c++ clang compiler-bug
asked Nov 15 at 18:25
HenrikS
148110
In order to force the execution of a template method at program start one can initialize a static member with a static method. Then the method is run at program start for every instantiation of the template class:
#include <cstdio>
template<typename t, t value>
struct dummy_user_t {};
template<int i>
struct my_struct_t
{
static int s_value;
// "use" s_value so it's initialized
using value_user_t = dummy_user_t<const int&, s_value>;
static int method()
{
printf("Hello %i!n", i);
return 0;
}
};
// initialize s_value with method() to run it at program start
template<int i>
int my_struct_t<i>::s_value {my_struct_t<i>::method()};
// instantiate my_struct_t
template struct my_struct_t<6>;
int main()
{
// nothing here
}
The output will be Hello 6!
This code compiles on all three major compilers but when you make s_value const it won't work in clang anymore (3.4 - 7.0) while still working in MSVC and GCC:
<source>:19:52: error: no member 'method' in 'my_struct_t<6>'; it has not yet been instantiated
const int my_struct_t<i>::s_value {my_struct_t<i>::method()};
^
<source>:10:51: note: in instantiation of static data member 'my_struct_t<6>::s_value' requested here
using value_user_t = dummy_user_t<const int&, s_value>;
^
<source>:21:17: note: in instantiation of template class 'my_struct_t<6>' requested here
template struct my_struct_t<6>;
^
<source>:11:16: note: not-yet-instantiated member is declared here
static int method()
^
1 error generated.
Try it out yourself:
With non const int: https://godbolt.org/z/m90bgS
With const int: https://godbolt.org/z/D3ywDq
What do you think? Is there any reason clang is rejecting this or is it a bug?
c++ clang compiler-bug
c++ clang compiler-bug
asked Nov 15 at 18:25
HenrikS
148110
asked Nov 15 at 18:25
HenrikS
148110
asked Nov 15 at 18:25
HenrikS
148110
asked Nov 15 at 18:25
HenrikS
148110
asked Nov 15 at 18:25
HenrikS
148110
148110
Move the explicit instantiation above the usage ofmy_struct_t<i>::method()andclangcompiles like a champ: godbolt.org/z/758iFF
– Swordfish
Nov 15 at 18:30
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
Another fix would be to move the type alias declaration beneath the definition ofmy_struct_t<i>::method().
– Swordfish
Nov 15 at 19:35
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Please re-read my last comment. You can have yourint constwithclangif you moveusing value_user_t = dummy_user_t<const int&, s_value>;to after the definition ofmethod().
– Swordfish
Nov 15 at 19:38
|
show 3 more comments
Move the explicit instantiation above the usage ofmy_struct_t<i>::method()andclangcompiles like a champ: godbolt.org/z/758iFF
– Swordfish
Nov 15 at 18:30
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
Another fix would be to move the type alias declaration beneath the definition ofmy_struct_t<i>::method().
– Swordfish
Nov 15 at 19:35
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Please re-read my last comment. You can have yourint constwithclangif you moveusing value_user_t = dummy_user_t<const int&, s_value>;to after the definition ofmethod().
– Swordfish
Nov 15 at 19:38
Move the explicit instantiation above the usage of
my_struct_t<i>::method() and clang compiles like a champ: godbolt.org/z/758iFF– Swordfish
Nov 15 at 18:30
Move the explicit instantiation above the usage of
my_struct_t<i>::method() and clang compiles like a champ: godbolt.org/z/758iFF– Swordfish
Nov 15 at 18:30
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
Another fix would be to move the type alias declaration beneath the definition of
my_struct_t<i>::method().– Swordfish
Nov 15 at 19:35
Another fix would be to move the type alias declaration beneath the definition of
my_struct_t<i>::method().– Swordfish
Nov 15 at 19:35
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Please re-read my last comment. You can have your
int const with clang if you move using value_user_t = dummy_user_t<const int&, s_value>; to after the definition of method().– Swordfish
Nov 15 at 19:38
Please re-read my last comment. You can have your
int const with clang if you move using value_user_t = dummy_user_t<const int&, s_value>; to after the definition of method().– Swordfish
Nov 15 at 19:38
|
show 3 more comments
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Move the explicit instantiation above the usage of
my_struct_t<i>::method()andclangcompiles like a champ: godbolt.org/z/758iFF– Swordfish
Nov 15 at 18:30
@Swordfish while that's true it defeats the purpose of being able to create new instantiation from anywhere in the code.
– HenrikS
Nov 15 at 18:33
Another fix would be to move the type alias declaration beneath the definition of
my_struct_t<i>::method().– Swordfish
Nov 15 at 19:35
Well, making s_value mutable isn't a big deal for my project. I was just curious which compiler is wrong.
– HenrikS
Nov 15 at 19:37
Please re-read my last comment. You can have your
int constwithclangif you moveusing value_user_t = dummy_user_t<const int&, s_value>;to after the definition ofmethod().– Swordfish
Nov 15 at 19:38