Basic reflection question

[EthernautParticipant]

If I have a string that contains the name of the class I want (let’s say, retrieved from a text file), how do I create an instance of that class?

Something along the lines of:

Monkey

[crayon-5cba87021f6c2083155071 inline="true" ] Local className := "MyClass" Local classInstance := CreateObjectFromString( className ) 'This is obviously a made up function

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[crayon-5cba87021f6c2083155071 inline="true" ] Local className := "MyClass" Local classInstance := CreateObjectFromString( className )  'This is obviously a made up function

[/crayon]

Cheers.

[Mark SiblyKeymaster]

Have you looked at the reflectiontest banana? There’s an exampole dynamically creating an object there…

[EthernautParticipant]

Ah, I had not looked into the examples.
Looking at it from Github now, seems like it will work like a charm.

Thanks!

[Mark SiblyKeymaster]

There is still some work to do on reflection, mostly ‘selective’ reflection. Currently reflection is ‘all or nothing’, and adds considerable size overhead to builds.

But this will happen eventually and apart from that I reckon it works well.

[EthernautParticipant]

One thing I also noticed is that the Reflection module doesn’t seem to be included at all in the “Modules Reference” page, so it’s hard to figure out which methods, properties, etc. are available.

Thanks Mark!

[EthernautParticipant]

Ok, still having some trouble, this time when trying to read the fields from a .json file and assign the values to the class fields.

It works fine if I just print the values and don’t actually assign them, but if you uncomment the lines that do the assignment I keep getting Memory access violations.

Here’s the json file. The class names are set for each Json object, in this format: “objectName:namespace.Class”

Monkey

{ "bob:test.Entity":{ "sort":0, "layer":1, "animation":"idle", "category":"npc", "position:test.Vec":{ "x":100, "y":50 }, "size:test.Vec":{ "x":30, "y":20 } } }

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{ "bob:test.Entity":{ "sort":0, "layer":1, "animation":"idle", "category":"npc", "position:test.Vec":{ "x":100, "y":50 }, "size:test.Vec":{ "x":30, "y":20 } } }

And here’s the Monkey2 code. Forgive me if it’s a little messy, I was in the middle of experimenting with this.

Monkey

Namespace test #Import "<std>" #Import "<reflection>" #Import "test.json" Using std.. Function Main() LoadFromFile( "asset::test.json" ) End '************************************************************************************************************************' Function LoadFromFile( path:String ) Local json := JsonObject.Load( path ) If json For Local entry := EachIn json.ToObject().Keys LoadFromMap( json[ entry ].ToObject(), entry ) Next End End Function LoadFromMap:Variant( obj:StringMap<JsonValue>, objType:String ) Local inst:Variant Local entry := objType.Split(":") If entry.Length <> 2 Then Print( "Error: Invalid format, entries should be 'name:Class'") Local newObj := TypeInfo.GetType( entry[1] ) If newObj Print( " ~n" + "New " + objType ) Local ctor := newObj.GetDecl( "New" ) 'This is the instance we'll assign the field values to inst = ctor.Invoke( Null, Null ) For Local key := EachIn obj.Keys Local d:= newObj.GetDecl( key ) 'If the field is an object, recursively call LoadFromMap If obj[key].IsObject 'Lets create the object, and return it so we can assign it to the appropriate field Local o := LoadFromMap( obj[key].ToObject(), key ) If inst = Null Then Print( "Error: no instance" ) If o = Null Then Print( "Error: no object" ) 'If o Then d.Set( inst, o ) '<--- This fails, even though 'inst' and 'o' exist 'If o Then d.Set( Cast<Entity>( inst ), Cast<Vec>( o ) )'<--- Just testing , didn't work either End 'Sweet! Now let's try to set the other fields! If obj[key].IsString Print( entry[0] + "." + key + ":String = '" + obj[key].ToString() + "'" ) d.Set( inst, obj[key].ToString() ) End If obj[key].IsNumber Print( entry[0] + "." + key + ":Number = " + obj[key].ToNumber() ) 'd.Set( inst, obj[key].ToNumber() ) '<------------------------ This fails unless there are no other fields End Next Else Print( "Error: Class " + objType + " not found" ) End If inst <> Null Return inst Else Print( "Error: Nothing to return" ) Return Null End End '************************************************************************************************************************ Class Entity Field name:String Field animation:String Field category:String Field layer:Double Field sort:Double Field size:Vec Field position:Vec End Class Vec Field X:Float Field Y:Float End

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Namespace test   #Import "<std>" #Import "<reflection>" #Import "test.json"   Using std..   Function Main() LoadFromFile( "asset::test.json" ) End   '************************************************************************************************************************'   Function LoadFromFile( path:String ) Local json := JsonObject.Load( path ) If json For Local entry := EachIn json.ToObject().Keys LoadFromMap( json[ entry ].ToObject(), entry ) Next End End   Function LoadFromMap:Variant( obj:StringMap<JsonValue>, objType:String ) Local inst:Variant   Local entry := objType.Split(":") If entry.Length <> 2 Then Print( "Error: Invalid format, entries should be 'name:Class'")   Local newObj := TypeInfo.GetType( entry[1] ) If newObj Print( " ~n" + "New " + objType ) Local ctor := newObj.GetDecl( "New" )   'This is the instance we'll assign the field values to inst = ctor.Invoke( Null, Null )   For Local key := EachIn obj.Keys Local d:= newObj.GetDecl( key ) 'If the field is an object, recursively call LoadFromMap If obj[key].IsObject 'Lets create the object, and return it so we can assign it to the appropriate field Local o := LoadFromMap( obj[key].ToObject(), key ) If inst = Null Then Print( "Error: no instance" ) If o = Null Then Print( "Error: no object" ) 'If o Then d.Set( inst, o ) '<--- This fails, even though 'inst' and 'o' exist 'If o Then d.Set( Cast<Entity>( inst ), Cast<Vec>( o ) )'<--- Just testing , didn't work either End   'Sweet! Now let's try to set the other fields! If obj[key].IsString Print( entry[0] + "." + key + ":String = '" + obj[key].ToString() + "'" ) d.Set( inst, obj[key].ToString() ) End If obj[key].IsNumber Print( entry[0] + "." + key + ":Number = " + obj[key].ToNumber() ) 'd.Set( inst, obj[key].ToNumber() ) '<------------------------ This fails unless there are no other fields End   Next Else Print( "Error: Class " + objType + " not found" ) End   If inst <> Null Return inst Else Print( "Error: Nothing to return" ) Return Null End End   '************************************************************************************************************************   Class Entity Field name:String Field animation:String Field category:String Field layer:Double Field sort:Double Field size:Vec Field position:Vec End   Class Vec Field X:Float Field Y:Float End

Any help appreciated!
Cheers.

[Mark SiblyKeymaster]

Ok, haven’t actually tried it but  I think the problem is here:

Local d:= newObj.GetDecl( key )

In the case of objects, ‘key’ will contain a ‘:’ char so GetDecl will be returning an ‘invalid’ decl as fields don’t have ‘:’ in their names.

This isn’t easy to spot, as the debugger is struggling a bit with ‘internal’ types like Decl, Variant etc!

A better approach may be to use a ‘class’ key in the json and leave field names ‘unmangled’.

[EthernautParticipant]

Yay, that worked! (after I cleaned it up and fixed another issue, the Vec class had X and Y fields capitalized, while the json file didn’t… took me forever to catch that one… )

Here’s the cleaned up json file:

Monkey

[crayon-5cba8702345ae242368566 inline="true" ] { "bob":{ "name":"Bob", "class":"test.Entity", "sort":0, "layer":1, "animation":"idle", "category":"npc", "position":{ "class":"test.Vec", "x":100, "y":50 }, "size":{ "class":"test.Vec", "x":30, "y":20 } } }

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[crayon-5cba8702345ae242368566 inline="true" ] { "bob":{ "name":"Bob", "class":"test.Entity", "sort":0, "layer":1, "animation":"idle", "category":"npc", "position":{ "class":"test.Vec", "x":100, "y":50 }, "size":{ "class":"test.Vec", "x":30, "y":20 } } }

[/crayon]

And here’s the example that uses it:

Monkey

[crayon-5cba8702345b3587439640 inline="true" ] Namespace test #Import "<std>" #Import "<reflection>" #Import "test.json" Using std.. Function Main() LoadFromFile( "asset::test.json" ) For Local e := Eachin Entity.all e.List() Next End '************************************************************************************************************************' Function LoadFromFile( path:String ) Local json := JsonObject.Load( path ) If json For Local entry := EachIn json.ToObject().Keys LoadFromMap( json[ entry ].ToObject(), entry ) Next End End Function LoadFromMap:Variant( obj:StringMap<JsonValue>, objName:String ) Local inst:Variant Local objClass:= obj["class"].ToString() Local newObj := TypeInfo.GetType( objClass ) If newObj Local ctor := newObj.GetDecl( "New" ) inst = ctor.Invoke( Null, Null ) 'This is the instance we'll assign the field values to. For Local key := EachIn obj.Keys If key = "class" Then Continue Local d:= newObj.GetDecl( key ) 'If the field is an object, recursively call LoadFromMap. If obj[key].IsObject Local o := LoadFromMap( obj[key].ToObject(), key ) If o Then d.Set( inst, o ) End 'Now let's try to set the other fields. If obj[key].IsString Then d.Set( inst, obj[key].ToString() ) If obj[key].IsNumber Then d.Set( inst, obj[key].ToNumber() ) If obj[key].IsBool Then d.Set( inst, obj[key].ToBool() ) Next Else Print( "Error: Class " + objClass + " not found" ) End If inst = Null Then Print( "Error: Nothing to return" ) Return inst End '************************************************************************************************************************ Class Entity Global all:= New Stack<Entity> Field name:String Field animation:String Field category:String Field layer:Double Field sort:Double Field size:Vec Field position:Vec Method New() all.Push( Self ) End Method List() Print "Entity:" Print "name = " + name Print "animation = " + animation Print "category = " + category Print "layer = " + layer Print "sort = " + sort Print "size = " + size.x + "," + size.y Print "position = " + position.x + "," + position.y End End Class Vec Field x:Double Field y:Double End

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[crayon-5cba8702345b3587439640 inline="true" ] Namespace test #Import "<std>" #Import "<reflection>" #Import "test.json" Using std.. Function Main() LoadFromFile( "asset::test.json" ) For Local e := Eachin Entity.all e.List() Next End '************************************************************************************************************************' Function LoadFromFile( path:String ) Local json := JsonObject.Load( path ) If json For Local entry := EachIn json.ToObject().Keys LoadFromMap( json[ entry ].ToObject(), entry ) Next End End Function LoadFromMap:Variant( obj:StringMap<JsonValue>, objName:String ) Local inst:Variant Local objClass:= obj["class"].ToString() Local newObj := TypeInfo.GetType( objClass ) If newObj Local ctor := newObj.GetDecl( "New" ) inst = ctor.Invoke( Null, Null ) 'This is the instance we'll assign the field values to. For Local key := EachIn obj.Keys If key = "class" Then Continue Local d:= newObj.GetDecl( key ) 'If the field is an object, recursively call LoadFromMap. If obj[key].IsObject Local o := LoadFromMap( obj[key].ToObject(), key ) If o Then d.Set( inst, o ) End 'Now let's try to set the other fields. If obj[key].IsString Then d.Set( inst, obj[key].ToString() ) If obj[key].IsNumber Then d.Set( inst, obj[key].ToNumber() ) If obj[key].IsBool   Then d.Set( inst, obj[key].ToBool() ) Next Else Print( "Error: Class " + objClass + " not found" ) End If inst = Null Then Print( "Error: Nothing to return" ) Return inst End '************************************************************************************************************************ Class Entity Global all:= New Stack<Entity> Field name:String Field animation:String Field category:String Field layer:Double Field sort:Double Field size:Vec Field position:Vec Method New() all.Push( Self ) End Method List() Print "Entity:" Print "name = " + name Print "animation = " + animation Print "category = " + category Print "layer = " + layer Print "sort = " + sort Print "size = " + size.x + "," + size.y Print "position = " + position.x + "," + position.y End End Class Vec Field x:Double Field y:Double End

[/crayon]

Mark, if you think this is good enough, feel free to use it as an example for the Reflection module (or for the Json module).

Do you think Reflection will ever allow generics? I’ll make special non-generic classes for now.
Thanks!

[Mark SiblyKeymaster]

Nice!

Do you think Reflection will ever allow generics?

Not sure yet, possibly, but it’ll never be able to ‘instantiate’ types that haven’t already been instantiated at compile time, so it’ll be more limited. eg: You wont be able to use Stack<Vec> if there isn’t a ‘compiled in’ one to begin with. But this is probably OK for many uses.

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