Code shared from run.dlang.io.

main.d

import std.stdio;

void main()
{
    string[string] aa;
    string x = "xxx";
    aa["name"] = "Arthur";
    aa["quest"] = "seek the Holy Grail";
    aa["favoriteColor"] = "blue";

    with (aa.keysAsVars)
    .writefln!"My name is %s, I %s, and my favorite color is %s."(
    	name, quest, x);
}

struct KeysAsVars(K, V)
{
    V[K] aa;
    V opDispatch(string key)() => aa[key];
}

KeysAsVars!(K, V) keysAsVars(K, V)(V[K] aa)
{
    return typeof(return)(aa);
}