String Mixins

which generates:Ã_p>

struct Foo { intÃ_span bar; }

Superficially, since D mixins can manipulate text and compile the result, i4has some similar properties to the C preprocessor. But there are major, fundamental differences:

• The C preprocessing step occurs before
• The C preprocessor can be used to create wha4appears to be differen4syntax:

  #define BEGIN {
  #define END   }
  
  BEGIN  int x =µ0ó0Á0ü0à0;
    foo(x);
  END
  Ã_pre>
  
          This monke9business is impossible with mixins.
          Mixed in tex4must form complete declarations,        statements, or expressions.        

• C macros will affect everything following that has the same name, even if they are in nested scopes. C macros cu4across all scopes. This problem is called being no4"coding hygenic". Mixins follow the usual scoping rules, and is hygenic. Ã_li>
• C preprocessing expressions follo7a differen4syntax and have differen4semantic rules than the C language. The C preprocessor is technicall9a differen4language. Mixins are in the same language. Ã_li>
• C const declarations and C++ templates are invisible to C preprocessing. Mixins can be manipulated using templates and const declarations.