Sigil Object Mapping - Basic Examples

1 - Map Arguments to Properties.cs

// Runnable from Linqpad 5
// Must install the Sigil nuget package and include the Sigil namespace

void Main()
{
	var createSample = GetMapperDelegate();
	
	// try it out
	createSample(23, "Hello").Dump();
}

static Func<int, string, Sample> GetMapperDelegate()
{
	// going to create a dynamic function which takes an int and string and assigns them
	// to the properties Id and Name of a new Sample object.

	// create emitter for the function
	var emit = Emit<Func<int, string, Sample>>.NewDynamicMethod("NewSample");

	// create a new Sample object and save it to a local variable
	var sample = emit.DeclareLocal<Sample>();
	emit.NewObject<Sample>(); // [newobj]
	emit.StoreLocal(sample);  // empty

	// assign Id
	emit.LoadLocal(sample);                                       // [sample]
	emit.LoadArgument(0);                                         // [sample] [id]
	emit.CallVirtual(typeof(Sample).GetProperty("Id").SetMethod); // empty

	// assign Name
	emit.LoadLocal(sample);                                         // [sample]
	emit.LoadArgument(1);                                           // [sample] [name]
	emit.CallVirtual(typeof(Sample).GetProperty("Name").SetMethod); // empty

	// return the object
	emit.LoadLocal(sample); // [sample]
	emit.Return();

	// we're done emitting IL, actually generate the function now
	return emit.CreateDelegate();
	
	// Note, we didn't really need to create a local variable, we could have used Duplicate()
	// to duplicate the top stack item every time we needed to use it before the return statemet.
	// The example below will use this methodology.
}

public class Sample
{
	public int Id { get; set; }
	public string Name { get; set; }
}

2 - Map Dictionary to Properties.cs

// Runnable from Linqpad 5
// Must install the Sigil nuget package and include the Sigil namespace

void Main()
{
	var createSample = GetMapperDelegate();

	// try it out
	createSample(new Dictionary<string, string>()
	{
		["One"] = "1",
		["Two"] = "22",
		["Three"] = "333",
		["Four"] = "4444",
	}).Dump();
	
	createSample(new Dictionary<string, string>()
	{
		["One"] = "Hello",
		["Three"] = "I didn't set every property.",
	}).Dump();
}

static Func<Dictionary<string, string>, Sample> GetMapperDelegate()
{
	// going to create a dynamic function which takes a Dictionary<string, string> and
	// for any string properties of Sample where there is a cooresponding key in the 
	// dictionary, we'll assign the dictionary value to the Sample property value.

	// create emitter for the function
	var emit = Emit<Func<Dictionary<string, string>, Sample>>.NewDynamicMethod("NewSample");
	const int DICTIONARY = 0;
	
	// get all of the public instance properties of sample
	var props = typeof(Sample).GetProperties(BindingFlags.Public|BindingFlags.Instance);
	
	// create a new Sample object
	emit.NewObject<Sample>(); // [sample]

	// use reflection to get the Dictionary<string, string>.TryGetValue method
	var paramTypes = new[] { typeof(string), typeof(string).MakeByRefType() }; // only necessary if there are overloads, but still good practice
	var tryGetValue = typeof(Dictionary<string, string>).GetMethod("TryGetValue", paramTypes);
	
	// declare local which we'll use for getting the output from TryGetValue
	var value = emit.DeclareLocal<string>();
	
	// for each property which is a string and has a setter, create code which looks for
	// that value in the dictionary.
	foreach (var prop in props)
	{
		if (prop.PropertyType != typeof(string) || prop.SetMethod == null)
			continue;
			
		// check the dictionary for a key matching the property name
		emit.LoadArgument(DICTIONARY); // [sample] [dict]
		emit.LoadConstant(prop.Name);  // [sample] [dict] [propName]
		emit.LoadLocalAddress(value);  // [sample] [dict] [propName] [ref value]
		// TryGetValue has signature "bool (this Dictionary, string, ref string)" so it consumes three values off the stack and pushes one
		emit.CallVirtual(tryGetValue); // [sample] [bool valueExists]
		
		// declare a label which will later mark the end of our if block
		var endIfLabel = emit.DefineLabel();
		
		// branch to the end of the if block if "valueExists" is false - consumes one stack value
		emit.BranchIfFalse(endIfLabel); // [sample]
		
		// inside the if block - now we can assign the found value to its corresponding property
		emit.Duplicate();                 // [sample] [sample]
		emit.LoadLocal(value);            // [sample] [sample] [value]
		// setter has signature "void (this Sample, string)" so it consumes two values off the stack and pushes nothing
		emit.CallVirtual(prop.SetMethod); // [sample]
		
		// mark the end of our if block
		emit.MarkLabel(endIfLabel);
	}
	
	// we're done assigning properties, now we just return the object (which is the only thing left on the stack)
	emit.Return();
	
	return emit.CreateDelegate();
}

public class Sample
{
	public string One { get; set; }
	public string Two { get; set; }
	public string Three { get; set; }
	public string Four { get; set; }
}

Some relevant discussion on http://nickcraver.com/blog/2016/02/17/stack-overflow-the-architecture-2016-edition/#comment-2521511736