c++11 - Removing mutations for D metaprogramming/compiletime array generation -

my plan write mutation-less code in d-language values available runtime. spoke me loop-unrolling , compile time code generation have no clear idea how that. have made d-template below has no guarantee evaluated @ compile-time because on 2 assignment statements(mutations) . advice appreciated. suggestions preferably in d or c++ without macros.

import std.stdio; import std.string; import std.conv;  const char[] alphabet="abfcdfrghdsthfg"; const string pattern="aba";   i[c]  computeatcompiletime(s ,c,i)( const s  pattern ){   i[c] table1;    const int size = to!int(pattern.length) ;//length of pattern matched    foreach( c; alphabet){   //initialise array           table1[c] = size;     }    foreach(i; 0..size-1){              table1[pattern[i]] = size -i-1;   }   return table1; } enum tablefromcompiler  = computeatcompiletime!(const string ,char, int)(pattern); void main(){      // enum tablefromcompiler  = computeatcompiletime!(const string ,char, int)(pattern);       writeln(tablefromcompiler);   } 

import std.stdio;  immutable char[] alphabet = "abfcdfrghdsthfg";  int[char] compute(in string pattern) {     int[char] table;      foreach (c; alphabet) {         table[c] = cast(int)pattern.length;     }      foreach (i, c; pattern) {         table[c] = cast(int)(pattern.length - - 1);     }      return table; }  void main() {     enum table = compute("aba");     writeln(table); } 

output:

['a':0, 'b':1, 'c':3, 'd':3, 'f':3, 'g':3, 'h':3, 'r':3, 's':3, 't':3] 

code on dpaste.