Question

How can I create a record type in F# by using reflection? Thanks

Answer 1

You can use FSharpValue.MakeRecord^[MSDN] to create a record instance, but I don’t think there’s anything baked into F# for defining record types. However, records compile to simple classes, so you could build a class as you would in C#. TypeBuilder^[MSDN] may be a good starting point.

UPDATE

Adding [<CompilationMapping(SourceConstructFlags.RecordType)>] to the type is all that’s required to make it a record. Here’s an example of how to do this at run-time.

let asmName = AssemblyName("Foo")
let asm = AppDomain.CurrentDomain.DefineDynamicAssembly(asmName, AssemblyBuilderAccess.RunAndCollect)
let moduleBldr = asm.DefineDynamicModule("Test")
let typeBldr = moduleBldr.DefineType("MyRecord", TypeAttributes.Public)
let attrBldr = CustomAttributeBuilder(
                typeof<CompilationMappingAttribute>.GetConstructor([|typeof<SourceConstructFlags>|]), 
                [|box SourceConstructFlags.RecordType|])
typeBldr.SetCustomAttribute(attrBldr)
let typ = typeBldr.CreateType()
printfn "%b" <| FSharpType.IsRecord(typ) //true