bmx-site/docs/api/brl/brl_reflection.md

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id: brl.reflection title: BRL.Reflection

sidebar_label: BRL.Reflection

Reflection

BlitzMax provides limited support for a form of runtime reflection.

Using reflection, programs can 'inspect' objects and types at runtime. You can determine the fields and methods contained in an object or type, set and get object fields and invoke - or 'call' - object methods.

To use reflection, you first need a TTypeId object. TTypeId objects correspond to BlitzMax user defined types, and there is a single TTypeId object for every user defined type in the program. There are also TTypeId objects for the 'primitive' types - byte, short, int, long, float, double and string. TTypeId objects are returned by the TTypeId.ForName and TTypeId.ForObject functions.

Once you have a TTypeId object, you can inspect the fields and methods of a user defined type using the EnumFields and EnumMethods methods. These methods return TField and TMethod objects that describe the fields and methods within the type. For example:

Strict

Type TMyType
	Field x,y,z
End Type

Local id:TTypeId=TTypeId.ForName( "TMyType" )

For Local fld:TField=EachIn id.EnumFields()
   Print fld.Name()+":"+fld.TypeId().Name()
Next
````

This simple program will print "x:Int", "y:Int" and "z:Int" - the names and types of the fields within TMyType. Note that this is done without actually creating a new TMyType.

The following example sets the fields of an object:

Strict

Type TMyType

Field x,y,z

End Type

Local obj:TMyType=New TMyType Local id:TTypeId=TTypeId.ForObject( obj )

For Local fld:TField=EachIn id.EnumFields()

fld.Set obj,String( Rand(10) )

Next

Print obj.x+","+obj.y+","+obj.z

In this case we need an actual instance of TMyType, otherwise we have nothing to set the fields of! Also, we have used TTypeId.ForObject instead of TTypeId.ForName to get a TTypeId. While in this case TTypeId.ForName could have been used to achieve the same result, in general we may not know the exact type of the object, and therefore we wont know its type name.

Also note that the code that actually sets the fields uses String( Rand(10) ). This is because the <b>Set</b> method takes an object - but our fields are ints! BlitzMax reflection deals with this by using strings to represent numeric types. The same rule applies to the <b>Get</b> method. Any numeric fields will be returned as strings which you must then convert to the appropriate type if necessary.

Finally, let's invoke an object method:
```
Strict

Type TMyType
	Method Update( t# )
		Print "TMyType.Update:"+t
	End Method
End Type

Local obj:TMyType=New TMyType
Local id:TTypeId=TTypeId.ForObject( obj )

Local update:TMethod=id.FindMethod( "Update" )

update.Invoke obj,[String( .25 )]

This example uses FindMethod to locate a type method and Invoke to call it. Arguments to the method are contained in an object array, and again the float argument is converted to a string.

In addition to the TTypeId, TField and TMethod types, the BlitzMax reflection module also declares a number of global TTypeId objects:

• ByteTypeId
• ShortTypeId
• IntTypeId
• LongTypeId
• FloatTypeId
• DoubleTypeId
• StringTypeId
• ObjectTypeId These may be used instead of the corresponding TTypeId.ForName call. For example, TTypeId.ForName( "Int" ) and IntTypeId will return the same object.

Types

Type	Description
TMember	Type member - Field Or Method.
TConstant	Type constant
TField	Type field
TGlobal	Type global
TFunction	Type function
TMethod	Type method
TTypeId	Type id

Globals

Global ByteTypeId:TTypeId

Primitive byte type

Global ShortTypeId:TTypeId

Primitive short type

Global IntTypeId:TTypeId

Primitive int type

Global UIntTypeId:TTypeId

Primitive unsigned int type

Global LongTypeId:TTypeId

Primitive long type

Global ULongTypeId:TTypeId

Primitive unsigned long type

Global FloatTypeId:TTypeId

Primitive float type

Global DoubleTypeId:TTypeId

Primitive double type