setting fields of object using traits

[Ram_B via Digitalmars-d-learn]

I'm trying to set fields of object from JSON with traits library. 
How i can to it properly?


import std.stdio;
import std.json;
import std.traits;
import std.meta:  Alias;

class Obj{
void fromJSON(this T)(JSONValue j){
foreach(field; FieldNameTuple!T){
alias member = Alias!(__traits(getMember, T, field));
static if (__traits(hasMember, member, "fromJSON")){
member.fromJSON(j[field]);
} else {
member = j[field];
}
}
}
}

class A : Obj{
int a,b;
C c;
this(){
c = new C();
}

}

class C : Obj{
int a;
this(){
a = 0;
};
}

int main(string[] argv)
{
string s = "{\"a\": 1, \"b\": 2, \"c\": {\"a\": 3} }";
JSONValue j = parseJSON(s);
A a = new A();
a.fromJSON(j);
writeln(a.b);
readln();
return 0;
}

main.d(14): Error: need 'this' for 'a' of type 'int'
main.d(14): Error: need 'this' for 'b' of type 'int'
main.d(12): Error: template main.Obj.fromJSON cannot deduce 
function from argument types !(c)(JSONValue), candidates are:

main.d(8):main.Obj.fromJSON(this T)(JSONValue j)
main.d(41): Error: template instance main.Obj.fromJSON!(A) error 
instantiating

Re: Metaprogramming with traits

[Ram_B via Digitalmars-d-learn]

On Friday, 16 September 2016 at 08:01:18 UTC, Gary Willoughby 
wrote:

On Thursday, 15 September 2016 at 22:05:55 UTC, Ram_B wrote:

test.d(33): Error: variable f cannot be read at compile time
test.d(33): Error: string expected as second argument of 
__traits hasMember instead of __error
test.d(46): Error: template instance test.A.t!(B) error 
instantiating


Maybe Array!(string) can't be use in compile-time code?


Which type of array i may use to pass it to compile-time function?

Re: Metaprogramming with traits

[Ram_B via Digitalmars-d-learn]

On Thursday, 15 September 2016 at 15:56:56 UTC, Gary Willoughby 
wrote:

On Thursday, 15 September 2016 at 15:07:09 UTC, Ram_B wrote:
How i can get fields of derived classes in runtime? This not 
works


What about something like this:

import std.traits;
import std.stdio;

class A {
int a,b;
this(){}
void fields(this T)(){
writeln(FieldNameTuple!(T));
foreach(Class; TransitiveBaseTypeTuple!(T)) {
writeln(FieldNameTuple!(Class));
}
}
}

class B : A{
int c;
this(){}
}

class C : B{
int d;
this(){}
}
void main(){
C c = new C();
c.fields();
}


This works, but i can't use (get|has)Member
class A{
int a, b;
Array!string fields(this T)(){
Array!string list;
foreach(field; FieldNameTuple!(T)){
list.insertBack(field);
}
foreach(Class; TransitiveBaseTypeTuple!(T)){
foreach(field; FieldNameTuple!(Class)){
list.insertBack(field);
}
}
return list;
}
void t(this T)(){
foreach(f; this.fields()){
log(__traits(hasMember, T, f)); 
}
}
}

class B : A{
int c;
this(){}
}

void main(){
B b = new B();
b.t();
}

test.d(33): Error: variable f cannot be read at compile time
test.d(33): Error: string expected as second argument of __traits 
hasMember instead of __error
test.d(46): Error: template instance test.A.t!(B) error 
instantiating

Re: Metaprogramming with traits

[Ram_B via Digitalmars-d-learn]

On Thursday, 15 September 2016 at 15:56:56 UTC, Gary Willoughby 
wrote:

On Thursday, 15 September 2016 at 15:07:09 UTC, Ram_B wrote:
How i can get fields of derived classes in runtime? This not 
works


What about something like this:

import std.traits;
import std.stdio;

class A {
int a,b;
this(){}
void fields(this T)(){
writeln(FieldNameTuple!(T));
foreach(Class; TransitiveBaseTypeTuple!(T)) {
writeln(FieldNameTuple!(Class));
}
}
}

class B : A{
int c;
this(){}
}

class C : B{
int d;
this(){}
}
void main(){
C c = new C();
c.fields();
}


Thanks very much! :3

Metaprogramming with traits

[Ram_B via Digitalmars-d-learn]

How i can get fields of derived classes in runtime? This not works

import std.traits;
import std.experimental.logger;


class A {
int a,b;
this(){}
void fields(){
log(FieldNameTuple!this);   
}
}

class B : A{
int c;
this(){}
}

void main(){
B b = new B();
b.fields();
}