OffsetOf

offset% = OffsetOf ( TypeName\field )

Returns the byte offset of field within TypeName, as a constant Int. Unlike AddressOf, this doesn't need a live instance, as it works directly off the type declaration

Type MyType
	Field A%
	Field B$
	Field C#
End Type

debuglog OffsetOf(MyType\A)   ; 0
debuglog OffsetOf(MyType\B)   ; 4
debuglog OffsetOf(MyType\C)   ; 8

Combine with AddressOf and PtrPeekInt/PtrPokeInt to reach a field from a raw object address instead of going through \field directly:

Local obj.MyType = New MyType
Local base% = AddressOf obj\A
Local bOffset% = OffsetOf(MyType\B)

PtrPokeInt base% + bOffset%, 123
debuglog obj\B   ; 123