Jaffe-

import std.stdio;
import std.algorithm;

struct S {
    int x[];

    void foo(int x) {
        this.x ~= x;
    }

Jaffe-

import std.stdio;

struct Test {
    int field1;
    string field2;
    double field3;
}

template make_fields(size_t SIZE, fields ...) {
    immutable string field = typeof(fields)[0].stringof ~ "[" ~ SIZE.stringof ~ "] " ~ fields[0].stringof ~ "; ";

Jaffe-

import std.stdio;

struct Test {
    int felt1;
    string felt2;
    double felt3;
}

template make_fields(int SIZE, fields ...) {
    immutable string base = typeof(fields)[0].stringof ~ "[" ~ SIZE.stringof ~ "] " ~ fields[0].stringof ~ "; ";