c++ template specialization and number of template arguments -

i have started learning templates, going through example typelist implemented , saw implementation of length method typelist.

template <class tlist> struct length; template <> struct length<nulltype> {     enum { value = 0 }; };  template <class t, class u> struct length< typelist<t, u> > {     enum { value = 1 + length<u>::value }; }; 

my question primary length template has 1 parameter (tlist) specialization has 2 parameters. how possible, read in other places specialization have less number of parameters

the first :

template <> struct length<nulltype> 

is full specialization, second:

template <class t, class u> struct length< typelist<t, u> > 

is partial specialization.

with full specialization give exact type on specialize. partial specialization allow types adheres restrictions, in case ability create type : typelist<t, u>, 2 template type arguments must provided.

for more details see here:

http://en.cppreference.com/w/cpp/language/template_specialization http://en.cppreference.com/w/cpp/language/partial_specialization

my question primary length template has 1 parameter (tlist) specialization has 2 parameters. how possible,

thats partial specialization allow, template parameter list must differ (for details see above link), must provide same number of type arguments primary template expects (length< typelist<t, u> >).