Convenient debug printing

[ezneh]

On Friday, 1 February 2019 at 15:49:24 UTC, Per Nordlöw wrote:
> [...]

Alright, after quite some work I finally managed to do the 
following code printing also nested variable names from classes & 
structs. I am not sure it's quite the same as the Rust AST macro 
for that, but I guess it's still interesting:

import std.stdio;

template dbg(args...)
{
	alias dbgImpl!(args).print dbg;
}

template dbgImpl(args...)
{
	import std.traits;
	void print(string file = __FILE__, uint line = __LINE__, string 
fun = __FUNCTION__)
	{
		static foreach (_; args)
		{
			static if(isBuiltinType!(typeof(_)))
				debug stderr.writefln("[%s:%s (%s)] %s = %s", file, line, fun,
					__traits(identifier, _), _);
			static if(isAggregateType!(typeof(_)))
			{
				debug stderr.writefln("[%s:%s (%s)] %s = %s", file, line, 
fun, __traits(identifier, _), toDbgString(_));
			}
		}
	}
	
	string toDbgString(Arg)(Arg o)
	{
		string dbgstr = "(";
		import std.format;
		static foreach(f; FieldNameTuple!(typeof(o)))
		{
			static if(isBuiltinType!(typeof(__traits(getMember, o, f))))
			{
				dbgstr ~= format("%s:%s, ", f, __traits(getMember, o, f));
			}
			static if(isAggregateType!(typeof(__traits(getMember, o, f))))
			{
				dbgstr ~= format("%s = %s, ", f, 
toDbgString(__traits(getMember, o, f)));
			}
		}
		return dbgstr[0..$-2] ~ ")";
	}
}
struct Foo{ int s = 2; bool b = false; Bar bar;}
struct Bar{ auto c = 'c';}
class FooBar{ int t; Foo f; }
void main()
{
	int i;
	float f = 3.14;
	string s = "some string";
	Foo foo;
	Bar bar;
	FooBar fb = new FooBar;
	dbg!(i, f, s, foo, 1+3, foo, bar, fb);
	
	// prints:
	// [dbg.d:54 (dbg.main)] i = 0
	// [dbg.d:54 (dbg.main)] f = 3.14
	// [dbg.d:54 (dbg.main)] s = some string
	// [dbg.d:54 (dbg.main)] foo = (s:2, b:false, bar = (c:c))
	// [dbg.d:54 (dbg.main)] _ = 4
	// [dbg.d:54 (dbg.main)] foo = (s:2, b:false, bar = (c:c))
	// [dbg.d:54 (dbg.main)] bar = (c:c)
	// [dbg.d:54 (dbg.main)] fb = (t:0, f = (s:2, b:false, bar = 
(c:c)))
}