why I cannot use forward declaration when using template？
1473
When can I use a forward declaration?
94572
Template within template: why "`>>' should be `> >' within a nested template argument list"
44265
What's the scope of the "using" declaration in C++?
19033
Error using a constexpr as a template parameter within the same class
118998
What are all the syntax problems introduced by the usage of angle brackets in C++ templates?
86296
Why can't we initialize members inside a structure?
150233
Why doesn't reference-to-member exist in C++?
33453
Why do I get "unresolved external symbol" errors when using templates?
99699
Why including same headers in multiple cpp files and then their compilation works?
78034
Is std::unique_ptr required to know the full definition of T?
55702
What are forward declarations in C++?
33156
C++ template won't accept iterators
91472
Why do I get syntax error when I try to run my C++ program after compiling it?
56989
Why is "using namespace std;" considered bad practice?
25103
Why can't I declare a friend through a typedef?
42432
"invalid use of incomplete type" error with partial template specialization
149350
'foo' was not declared in this scope c++