C ++ implements multi-parameter addition and comparison similar to Common Lisp

In CL, we can do this:

1 $ sbcl2 * (+ 1 2 3)3 64 * (< 1 2 3)5 T6 * (< 2 3 1)7 NIL8 * 

In simple terms, the + and <of CL is a function that receives multiple parameters, a bit similar to the add (, 3) and less (, 3) of cpp.

Therefore, after the variable parameter template is available in C ++ 11, you can add multiple parameters and compare multiple parameters.

 1 #include <functional> 2 template<typename O, typename A,typename B> 3 bool cmp(O o, A a,B b){ 4     return o(a, b); 5 } 6 template<typename O, typename A,typename B,typename... C> 7 bool cmp(O o,A a,B b,C... c){ 8     return o(a, b) and cmp(o,b,c...); 9 }10 template<typename O, typename A,typename B>11 A reduce(O o, A a,B b){12     return o(a, b);13 }14 template<typename O, typename A,typename B,typename... C>15 A reduce(O o,A a,B b,C... c){16     return reduce(o,o(a, b),c...);17 }18 19 bool foo(int a,int b,int c,int d){20   return cmp(std::less<int>(), a,b,c,d);21 }22 int bar(int a,int b,int c,int d){23   return reduce(std::plus<int>(), a,b,c,d);24 }

Some people may say that this is not a pitfall. no matter whether the writing method is ugly than CL, you still call it recursively. It's so weak .....

Let's look at the truth (clang ):

 1 foo(int, int, int, int):                             # @foo(int, int, int, int) 2     cmpl    %esi, %edi 3     jge    .LBB0_1 4     cmpl    %edx, %esi 5     setl    %sil 6     cmpl    %ecx, %edx 7     setl    %al 8     andb    %sil, %al 9     ret10 .LBB0_1:11     xorl    %eax, %eax12     ret13 14 bar(int, int, int, int):                             # @bar(int, int, int, int)15     addl    %esi, %edi16     leal    (%rdi,%rdx), %eax17     addl    %ecx, %eax18     ret

It's no different from handwriting. Oh, it's a little ugly, but it's definitely slower than C ++ to read the CL compilation... (Escape

Finally, what is the purpose?

Multi-parameter addition seems useless. It is better to write a + B + c + d.
Multiple parameters are okay.

A <B and B <c and c <d