Comments (6)
Because it should never be necessary to instantiate the base template. As the static_assert
error message says, you need to specialize the traits for each type you are using.
Using sizeof(T)==0
is a trick to make the line depend on the template parameter and which always yields false
(since no type can have a size of 0), so you get a nice compile-time error message when you instantiate (aka use) the template with a type without specializing it first. If I would just write static_assert( false, "..." );
, the error would appear immediately when compiling the template itself. The error must be deferred until it is instantiated, hence the dependency on a template parameter is required.
from json.
We experienced this issue when trying to use the library with MSVC 2015. Everything seems to work fine, but this assertion is triggered. We definitely can't be using the traits::assign() function though, since surely that would generate a link time error?
from json.
If the assert triggers, it means you forgot to specialize the traits function. Look at the error message, what it T
? (The compiler will usually tell you)
That is the type you are trying to use, but there is no traits specialization for that type, hence the library doesn't know what to do with it. The static_assert
must trigger to notify you of a problem in your code.
If you can post the error message and a small code example/excerpt, I might be able to help further...
from json.
what it T? (The compiler will usually tell you)
The visual studio compiler is not giving us any useful information.
I commented out all the code that uses your lib but only include the header. The compile output is
c:\projects\app\third_party\json\include\tao\json\traits.hpp(32): error C2338: no traits specialization found c:\projects\app\third_party\json\include\tao\json/value.hpp(118): note: see reference to class template instantiation 'tao::json::traits<std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>,void>' being compiled with [ _Kty=std::string, _Ty=tao::json::basic_value<tao::json::traits> ] C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE\xtree(1444): note: while compiling class template member function 'std::_Tree_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>> std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,false>>::erase(std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>,std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>)' with [ _Kty=std::string, _Ty=tao::json::basic_value<tao::json::traits>, _Pr=std::less<std::string>, _Alloc=std::allocator<std::pair<const std::string,tao::json::basic_value<tao::json::traits>>> ] C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE\xtree(2168): note: see reference to function template instantiation 'std::_Tree_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>> std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,false>>::erase(std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>,std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>)' being compiled with [ _Kty=std::string, _Ty=tao::json::basic_value<tao::json::traits>, _Pr=std::less<std::string>, _Alloc=std::allocator<std::pair<const std::string,tao::json::basic_value<tao::json::traits>>> ] C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE\map(73): note: see reference to class template instantiation 'std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,false>>' being compiled with [ _Kty=std::string, _Ty=tao::json::basic_value<tao::json::traits>, _Pr=std::less<std::string>, _Alloc=std::allocator<std::pair<const std::string,tao::json::basic_value<tao::json::traits>>> ] c:\projects\app\third_party\json\include\tao\json/value.hpp(868): note: see reference to class template instantiation 'std::map<std::string,tao::json::basic_value<tao::json::traits>,std::less<_Kty>,std::allocator<std::pair<const _Kty,_Ty>>>' being compiled with [ _Kty=std::string, _Ty=tao::json::basic_value<tao::json::traits> ] c:\projects\app\third_party\json\include\tao\json/from_string.hpp(78): note: see reference to class template instantiation 'tao::json::basic_value<tao::json::traits>' being compiled
I don't feel the error message is accurate :(
from json.
Ah, I see. Well, the error message is basically complaining about a missing specialization for
std::map< std::string, tao::json::basic_value< tao::json::traits > >::const_iterator
but that is most likely a problem in our code. As we are not Visual Studio / Windows users ourselves and the library is in an early stage of development, we haven't found the time to make it compatible with Visual Studio. I know, bad news... sorry.
I am about to refactor some more stuff (probably later today), maybe it solves the problem, maybe not. Probably not. :-/ Anyways, I'm afraid there is no real solution currently. After the next refactoring, we would, of course, appreciate help from actual Visual Studio users if they can figure out ways to fix the problems VS is having and send a pull request. I'll close the question for now, general Visual Studio / Windows support will happen anyways when we have enough time and help in the future.
from json.
Sure, thank you very much for all the help. Enjoy coding :D
from json.
Related Issues (20)
- How to write cbor/jaxn/msgpack and other file ? HOT 1
- demangle.hpp build failure for MSVC HOT 1
- How can we improve tao-json performance ? HOT 2
- transforming unsigned to chrono::duration HOT 2
- the conan package at https://conan.io/center/taocpp-json missing to/from_nolhmann.hpp files HOT 2
- Stack-overflow occured when parsing a bad json file HOT 2
- why isn't to/from_nolhmann.hpp files are excluded from contrib folder on release HOT 1
- Binding questions HOT 14
- Issues using 1.0.0-beta.13 with C++20 HOT 5
- About the first stable version of Taojson HOT 1
- looks like `tao::json::value::operator[]` doesn't accept string as a key HOT 3
- simple json program won't compile on raspberry pi bullseye HOT 6
- feature request: std::string_view as first argument to TAO_JSON_BIND_REQUIRED HOT 3
- `rewind_mode::dontcare` not implemented in PEGTL? HOT 1
- Reset Event consumer? HOT 2
- Question: conditionally group bindings in a trait?
- json main cannot be compiled with PEGTL main
- Question: nesting binding::object in one binding trait definition possible/supported? HOT 3
- traits: ability to define what optional means HOT 7
- Benchmarks? HOT 8
Recommend Projects
-
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
-
Vue.js
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
-
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
-
TensorFlow
An Open Source Machine Learning Framework for Everyone
-
Django
The Web framework for perfectionists with deadlines.
-
Laravel
A PHP framework for web artisans
-
D3
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
-
Recommend Topics
-
javascript
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
-
web
Some thing interesting about web. New door for the world.
-
server
A server is a program made to process requests and deliver data to clients.
-
Machine learning
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
-
Visualization
Some thing interesting about visualization, use data art
-
Game
Some thing interesting about game, make everyone happy.
Recommend Org
-
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
-
Microsoft
Open source projects and samples from Microsoft.
-
Google
Google ❤️ Open Source for everyone.
-
Alibaba
Alibaba Open Source for everyone
-
D3
Data-Driven Documents codes.
-
Tencent
China tencent open source team.
from json.