c++ - uniqueness of struct names -

while name of structure must unique in set of structures within namespace, such name can "shared" variables , functions. example, following code compiles fine:

// code 1 struct h{}; int h{ 8 }; 

similarly, there no collision in:

// code 2 struct h{}; void h(){} 

1) reasoning allow name sharing?

moreover, if throw templates mix, have strange situations. code

// code 3 template< class h > void h(){} struct h{}; template< class h > struct j{}; void j(){} 

does compile; following code fails:

// code 4 struct h{}; template< class h > void h(){} void j(){} template< class h > struct j{}; 

2) why reasoning allowed code 2 not enough allow code 4? not asking rules in standard. asking reason behind rules.

1) reasoning allow name sharing?

according "the design , evolution of c++", bjarne stroustrup, section 2.8.2 "structure tags vs. type names", feature introduced maintain compatibility c. c language requires use of struct keyword name structure (no keyword required name typedef). can use same identifier declare structure , either function or variable:

struct x { int m; }; void x(void);  x(); // call x struct x x; // create new object of type x 

a significant syntactic simplification benefit of users introduced c++ @ cost of work implementers , c compatibility problems. [...] in context of c classes [dyp: predecessor of c++], had annoyed me time because made user-defined types second-class citizens syntactically.

[...]

the real need address particular issue came fact standard unix header files, notably, stat.h, rely on struct , variable or function having same name.

-- d&e 2.8.2

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2) why reasoning allowed code 2 not enough allow code 4?

i'll first quote c++11 standard:

a class template shall not have same name other template, class, function, variable, enumeration, enumerator, namespace, or type in same scope (3.3), except specified in (14.5.5 [dyp: class template partial specialization]). except function template can overloaded either (non-template) functions same name or other function templates same name (14.8.3 [dyp: refers overloading]), template name declared in namespace scope or in class scope shall unique in scope.

-- c++11 international standard [temp]p5

according interpretation of passage, codes 3 , 4 both illegal. clang++ rejects them, accepts first part of code 3:

template< class h > void h(){} struct h{}; 

which, according [temp]p5, should illegal well.

considering these examples (3, 4, , beginning of 3) illegal, think rationale don't need compatibility exception in cases: c has no templates.