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  1. #include <iostream>
  2. #include <cstdlib>
  3. #include <cassert>
  4. using namespace std;
  5.  
  6. struct rgba
  7. {
  8.     uint8_t r, g, b, a;
  9.  
  10.     constexpr uint8_t& operator[](size_t x)
  11.     {
  12.         return const_cast<uint8_t*>(&r)[x];
  13.     }
  14. };
  15.  
  16. struct rgba2
  17. {
  18.     uint8_t r, g, b, a;
  19.  
  20.     constexpr uint8_t& operator[](size_t x)
  21.     {
  22.     	assert(x>=0 && x<4);
  23.     	switch (x){
  24.     		case 0: return r; 
  25.     		case 1: return g;  
  26.     		case 2: return b;  
  27.     		case 3: return a; 
  28.     		//default: throw(1);  // not possible with constexpr
  29.     	}
  30.     }
  31. };
  32.  
  33. struct rgba3
  34. {
  35. 	enum ergb { red, green, blue, alpha};
  36.     uint8_t c[alpha+1];
  37.  
  38.     constexpr uint8_t& operator[](ergb x)
  39.     {
  40.      	assert(x>=0 && x<4);
  41.      	return c[x];
  42.     }
  43. };
  44.  
  45.  
  46. int main() {
  47. 	// your code goes here
  48. 	rgba2 cola;
  49. 	rgba3 colb; 
  50. 	cola[1]=2;
  51. 	colb[rgba3::green]=3;
  52.  
  53. 	return 0;
  54. }
Success #stdin #stdout 0s 3452KB
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stdout 
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https://ideone.com/u8lvtx
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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