c++ - Assert when instancing specific template specialization -


By default, a user can specifically write a template, by adding some useful error messages to the default template: 

  template & lt; Typename T & gt; Struct foo {static_assert (sizeof (t)! = Sizeof (T), "Please specialize in foo for your type"); };   
 Since always-false conditions depend on a template parameter, that firmness will be evaluated only during the template reversal, whatever we want.  
 Now consider the inverse case: We allow the user to use the generic version of the template, but do not allow it to use a specific rebound. For example:  
  template & lt; Typename T & gt; The Straight Bar {/ * Something useful for the user; The template's & lt; & Gt; Straight bar & lt; Char & gt; {Static_assert (wrong, "no, you can not instantiate time with the bar"); };   
 Of course this does not work because the claim is not dependent on a template parameter, even then the compilation will fail, even if the user has  the bar & lt; Char & gt; / Code>.  
 My question is:  Is there any way to evaluate that kind of expression unless the template installation?   
  Edit : A more complex example:  
  template & lt; Typename T & gt; Struct quux {/ * Something useful for the user; / * This specialization has been defined which rejects any example of quux which uses * templates with * * templates, such as parameter * / template & lt; Template & lt; Typename & gt; Class T & gt; Structure quacks & lt; T & lt; Bool & gt; & Gt; {Static_assert ("wrong," please do not use quix with a template with the bool parameter); };    
 
 
 No special expertise required:  
  Template & lt; Typnam T & G; Structure bar {static_assert (! Std :: is_same & lt; T, char & gt; :: value, "No, you can not instantiate times with the bar"); }; Edit: In response to your edit, again the same thing:  
  Template   Template & lt; Typename & gt; Class T, Typanum U & gt; Structure quacks & lt; T & lt; U & gt; & Gt; {Static_assert (! Std :: is_same & lt; U, bool & gt; :: value, "please do not use quux with a template with bux parameter"); };

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