d转换元组为数组

Posted 2022-09-03 fqbqrr

假定,​​std.typecons.Tuple​​​,可用​​[tup.expand]​​​从元组造数组.​​[valSeq]​​​搞值序列.
如下搞数组的数组:

auto arrayOfArrays = [ keys, values ];

更通用的:

import std;
//编译慢但是很方便
auto makeTestTuple(int i) 
  return tuple!("key", "value")((i * 2).to!string,(double(i) / 10).to!string);


void main() 
  auto tuples = iota(10)
                .map!makeTestTuple
                .array;

  string[] keys;
  string[] values;

  writeln("命令式:");

  foreach (t; tuples) 
    keys ~= t.key;
    values ~= t.value;
  

  writeln(keys);
  writeln(values);

  writeln("替代方案:");
  keys = tuples.map!(t => t.key).array;
  values = tuples.map!(t => t.value).array;
  writeln(keys);
  writeln(values);

  writeln("更通用:");
  keys = tuples.memberArray!"key";
  values = tuples.memberArray!"value";
  writeln(keys);
  writeln(values);


auto memberArray(string member, T)(T[] tuples) 
  return tuples.map!(t => mixin("t." ~ member)).array;

第2个程序:

import std;

auto makeTestTuple(int i) 
  return tuple!("key", "value", "其他")(
    (i * 2).to!string,
    (double(i) / 10).to!string,
    i * i);


mixin template matchingMember(string name, T) 
  mixin (T.stringof ~ "[] " ~ name ~ ;);


template TupleMemberArrays(T) 
  alias types = T.Types;
  alias fieldNames = T.fieldNames;
  enum memberCount = types.length;

  struct TupleMemberArrays 
    static foreach (i; 0 .. memberCount) 
      mixin matchingMember!(fieldNames[i], types[i]);
    

    this(T[] tuples) 
      foreach (t; tuples) 
        static foreach (i; 0 .. memberCount) 
          mixin (format!q
              %s ~= t.%s = t[%s];
            (fieldNames[i], fieldNames[i], i));
        
      
    
  


void main() 
  auto tuples = iota(10)
                .map!makeTestTuple
                .array;

  alias S = TupleMemberArrays!(ElementType!(typeof(tuples)));
  auto s = S(tuples);
  writeln(s.key);
  writeln(s.value);
  writeln(s.其他);

第二个程序定义了​​匹配元组成员​​​的类型.给定成员名为​​"key","value"​​​和​​"其他"​​​的元组;及串,串,整​​类型​​​;生成类似以下​​结构​​:

struct YourAliasHere 
  string[] key;
  string[] value;
  int[] 其他;

限制:该实现使用​​并非​​​所有元组都使用的​​字段名​​​.但在需要时,可更改为生成​​field0,field1​​等.