Multiple iterators over single container

two_iterator_kinds.cpp

#include <cstdio>
using namespace std;

struct range
{
	int a, b;

	struct n_iter
	{
		int x;
		int operator*() const { return x; }
		bool operator!=(const n_iter y) const { return x != y.x; }
		n_iter &operator++() { x++; return *this; }
	};
	struct sq_iter
	{
		int x;
		int operator*() const { return x*x; }
		bool operator!=(const sq_iter y) const { return x != y.x; }
		sq_iter &operator++() { x++; return *this; }
	};

	template <typename T>
	struct proxy
	{
		const range &orig;
		T begin() const { return { orig.a }; }
		T end() const { return { orig.b }; }
	};

	proxy<n_iter> numbers() { return {*this}; }
	proxy<sq_iter> squares() { return {*this}; }
};

int main()
{
	range r{ 1, 5 };
	for (auto x : r.numbers())
	{ printf("%d\n", x); }
	for (auto x : r.squares())
	{ printf("%d\n", x); }
	return 0;
}

two_iterator_kinds.s

    .file   "zoom.cpp"
    .section    .rodata.str1.1,"aMS",@progbits,1
.LC0:
    .string "%d\n"
    .section    .text.unlikely,"ax",@progbits
.LCOLDB1:
    .section    .text.startup,"ax",@progbits
.LHOTB1:
    .p2align 4,,15
    .globl  main
    .type   main, @function
main:
.LFB22:
    .cfi_startproc
    pushq   %rbx
    .cfi_def_cfa_offset 16
    .cfi_offset 3, -16
    movl    $1, %ebx
.L2:
    movl    %ebx, %esi
    xorl    %eax, %eax
    movl    $.LC0, %edi
    addl    $1, %ebx
    call    printf
    cmpl    $5, %ebx
    jne .L2
    movl    $1, %esi
    movl    $.LC0, %edi
    xorl    %eax, %eax
    call    printf
    movl    $4, %esi
    movl    $.LC0, %edi
    xorl    %eax, %eax
    call    printf
    movl    $9, %esi
    movl    $.LC0, %edi
    xorl    %eax, %eax
    call    printf
    movl    $16, %esi
    movl    $.LC0, %edi
    xorl    %eax, %eax
    call    printf
    xorl    %eax, %eax
    popq    %rbx
    .cfi_def_cfa_offset 8
    ret
    .cfi_endproc
.LFE22:
    .size   main, .-main
    .section    .text.unlikely
.LCOLDE1:
    .section    .text.startup
.LHOTE1:
    .ident  "GCC: (exherbo gcc-4.9.2) 4.9.2"
    .section    .note.GNU-stack,"",@progbits