On 2016-05-23 21:00, Adam D. Ruppe wrote:
Have I gone completely mad?!?!
---
void main() {
import std.stdio;
writeln(obj!(
foo => "bar",
baz => 12
));
}
---
Prints out:
{
foo: bar
baz: 12
}
A few tweaks would make a whole loose typed hash thing more akin to Ruby
or PHP than D. What's obj? Behold:
string obj(T...)() {
import std.conv, std.traits;
string jsonResult = "{";
foreach(arg; T) {
jsonResult ~= "\n\t";
// I don't know why the usual is(__parameters) trick
// won't work here, but a stringof hack will!
string hack = typeof(arg!string).stringof;
import std.string;
hack = hack[hack.indexOf("function(string ") +
"function(string ".length .. $];
hack = hack[0 .. hack.indexOf(")")];
jsonResult ~= hack;
jsonResult ~= ": ";
jsonResult ~= to!string(arg(""));
}
jsonResult ~= "\n}";
return jsonResult;
}
That's pretty cool and pretty ugly :).
As you probably know, D has a couple lambda literal syntaxes. One of
these is the fat arrow, with a valid form of argument => return_expression.
The compiler makes templates out of these when you pass them around....
and those templates contain the parameters, including the name, and are
callable code (if instantiated with a concrete type).
I was disappointed to see the ordinary reflection tools didn't work here
- I know, I'm abusing the language - but the trusty old .stringof hack
did! Combined with the magic knowledge that these things are templates,
I instantiated them (tbh I was a bit surprised it actually let me!) and
extracted the name of the argument.
__parameters doesn't work because an "untyped" lambda is a template and
__parameters works with functions, but I guess you already know that.
Instantiating the lambda and then using __parameters should work.
There's a PR for DMD which adds support for inspecting template
parameters [1] that would help. Unfortunately it's closed.
Here's a version building an associative array mapping strings to variants:
import std.stdio : println = writeln;
import std.variant;
Variant[string] hash(T...)() {
import std.conv, std.traits;
Variant[string] aa;
foreach(arg; T) {
// I don't know why the usual is(__parameters) trick
// won't work here, but a stringof hack will!
string hack = typeof(arg!string).stringof;
import std.string;
hack = hack[hack.indexOf("function(string ") + "function(string
".length .. $];
hack = hack[0 .. hack.indexOf(")")];
aa[hack] = Variant(arg(""));
}
return aa;
}
void main() {
auto h = hash!(
foo => 3,
bar => "asd"
);
writeln(h);
}
[1] https://github.com/dlang/dmd/pull/5201
--
/Jacob Carlborg
