Discussion: lightweight dynamic

[alrz]

Moved from dotnet/roslyn#16077

This can be a lightweight compile-time alternative to System.Dynamic.DynamicObject,

var r = obj.$Property;
var r = obj["Property"]; // indexer is prefered over TryGetProperty
var r = obj.TryGetProperty("Property");

obj.$Property = value;
obj["Property"] = value; // indexer is prefered over TrySetProperty
obj.TrySetProperty("Property", value);

var r = obj.$Method();
var r = obj.TryInvoke("Method", Array.Empty<Argument>());

var r = obj.Method$();
var r = obj.Method(Array.Empty<Argument>());

Open question: should we implicitly cast the result to the target type?

string r = obj.$Property;
string r = obj["Property"] as string;

Related: dotnet/roslyn#3555

[fanoI]

It surely would semplify the use Dictionaries, json and so on... I'm less sure that this have sense:

var r = obj.$Method();

why not simply call the method directly?

[HaloFour]

Are you also suggesting a new object model for dynamic types as an alternative to System.Dynamic? Otherwise I don't get the point. Seems like in most cases it's just an alternative syntax to using an indexer which provides no real benefits to consumption. It's been argued that the IDE could provide some degree of autocomplete, but I don't see why that wouldn't also be the case for supplying an argument to an indexer for a known type.

[alrz]

@HaloFour

Are you also suggesting a new object model for dynamic types as an alternative to System.Dynamic?

System.Dynamic.DynamicObject depends on DLR, but this would use the statically resolved members.

@fanoI

why not simply call the method directly?

When you want to handle calls as "messages" and you don't have a fixed scheme this'll help. obj.Method$(); variant allows you to call an existing method but with a dynamic argument list which would be passed in the form of new Argument(name: .. , value: ... ). These are possible using dynamic or a custom System.Dynamic.DynamicObject but, as I said, it depends on DLR and involves run-time cost.

[HaloFour]

@alrz

If it's relying on either an indexer or some Try method then it's not statically resolved, at least not anymore than dynamic currently is. It is certainly more lightweight than DynamicObject and IDynamicMetaObjectProvider but it completely duplicates that functionality.

[GeirGrusom]

Sounds a little like D's forwarding operator.

[alrz]

If it's relying on either an indexer or some Try method then it's not statically resolved

I meant the Try methods themselves. Even though Try methods in a DynamicObject are somehow known to the DLR, the compiler needs to emit dynamic call-sites for dynamic objects.