• BlackEdder (12/12) Jul 25 2014 Is it possible to automatically convert an associative array to a
• bearophile (7/8) Jul 25 2014 I think it's possible, as long as your associative array contents
• John Colvin (16/29) Jul 25 2014 one possible way:
• BlackEdder (26/62) Jul 25 2014 The associative array is actually not known at compile time. I

"BlackEdder" <edder tkwsping.nl> writes:

Is it possible to automatically convert an associative array to a
struct?

Basically I want to do the following (for any struct).

struct A {
     double x = 1;
}

double[string] aa = ["x":1];

auto a = toStruct!A( aa );

I've been trying to do this at compile time, but can't work out
how setMembers and or loop over the associative array at compile
time.

Is this possible at all?

"bearophile" <bearophileHUGS lycos.com> writes:

BlackEdder:

 Is this possible at all?

I think it's possible, as long as your associative array contents 
are known at compile-time. You can write a function that given 
the associative array returns a string that mixed-in defines the 
struct. And then you can define a toStruct template.

Bye,
bearophile

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Friday, 25 July 2014 at 15:25:43 UTC, BlackEdder wrote:
 Is it possible to automatically convert an associative array to 
 a
 struct?

 Basically I want to do the following (for any struct).

 struct A {
     double x = 1;
 }

 double[string] aa = ["x":1];

 auto a = toStruct!A( aa );

 I've been trying to do this at compile time, but can't work out
 how setMembers and or loop over the associative array at compile
 time.

 Is this possible at all?

one possible way:

enum aa = ["x": 1];
import std.traits;

struct AAtoStruct(alias aa)
     if(isAssociativeArray!(typeof(aa)) && 
isSomeString!(KeyType!(typeof(aa))))
{
     alias T = ValueType!(typeof(aa));
	
     import std.range, std.algorithm, std.array;
     mixin(zip(aa.keys, aa.values)
           .map!`"T " ~ a[0] ~ " = " ~ a[1].to!string ~ ";\n"`
           .joiner.array);
}

alias S = AAtoStruct!aa;

"BlackEdder" <edder tkwsping.nl> writes:

On Friday, 25 July 2014 at 15:48:54 UTC, John Colvin wrote:
 On Friday, 25 July 2014 at 15:25:43 UTC, BlackEdder wrote:
 Is it possible to automatically convert an associative array 
 to a
 struct?

 Basically I want to do the following (for any struct).

 struct A {
    double x = 1;
 }

 double[string] aa = ["x":1];

 auto a = toStruct!A( aa );

 I've been trying to do this at compile time, but can't work out
 how setMembers and or loop over the associative array at 
 compile
 time.

 Is this possible at all?

 one possible way:

 enum aa = ["x": 1];
 import std.traits;

 struct AAtoStruct(alias aa)
     if(isAssociativeArray!(typeof(aa)) && 
 isSomeString!(KeyType!(typeof(aa))))
 {
     alias T = ValueType!(typeof(aa));
 	
     import std.range, std.algorithm, std.array;
     mixin(zip(aa.keys, aa.values)
           .map!`"T " ~ a[0] ~ " = " ~ a[1].to!string ~ ";\n"`
           .joiner.array);
 }

 alias S = AAtoStruct!aa;

The associative array is actually not known at compile time. I 
got it working though:

unittest {
   T toStruct( T )( double[string] aa ) {
     T t;
     foreach (name; __traits(allMembers, T))
     {
       static if(
           __traits(compiles, __traits(getMember, t, name))
           //  Skip Functions
           && !isSomeFunction!(__traits(getMember, t, name) )
           )
       {
         mixin( "t." ~ name ~ "= aa[\"" ~ name ~ "\"];" );
       }
     }
     return t;
   }

   struct A {
     double x = -1;
  }

  double[string] aa = ["x":1];

  auto a = toStruct!A( aa );

  assert( a.x == 1 );
}