Creating record type in F#
f#, type-providers
Solution
Putting aside the usefulness of the end result, a snippet below achieves exactly what you asked for in the spirit of my other related answer:
#if INTERACTIVE
#r @"C:\Program Files (x86)\Microsoft F#\v4.0\FSharp.Compiler.dll"
#r @"C:\Program Files (x86)\FSharpPowerPack-1.9.9.9\bin\FSharp.Compiler.CodeDom.dll"
#endif
open System
open System.CodeDom.Compiler
open Microsoft.FSharp.Compiler.CodeDom
open Microsoft.FSharp.Reflection
type RecordTypeMaker (typeName: string, records: (string*string) []) =
let _typeDllName = "Synth"+typeName+".dll"
let _code =
let fsCode = new System.Text.StringBuilder()
fsCode.Append("module ").Append(typeName).Append(".Code\ntype ").Append(typeName).Append(" = {") |> ignore
for rec' in records do fsCode.Append(" ").Append(fst rec').Append(" : ").Append(snd rec').Append(";\n") |> ignore
fsCode.Append("}").ToString()
let _compiled =
use provider = new FSharpCodeProvider()
let options = CompilerParameters([||], _typeDllName)
let result = provider.CompileAssemblyFromSource( options, [|_code|] )
result.Errors.Count = 0
let mutable _type: Type = null
member __.RecordType
with get() = if _compiled && _type = null then
_type <- Reflection.Assembly.LoadFrom(_typeDllName).GetType(typeName+".Code+"+typeName)
_type
A sketch implementation of `RecordTypeMaker` accepts an arbitrary `Record type` definition containing `type name` and array of `field names` accompanied by `field type names`. Then behind the curtain it assembles a piece of F# code defining the requested Record type, compiles this code via `CodeDom provider`, loads container assembly and provides access to this newly created synthetic Record type via Reflection. A test snippet
let myType = RecordTypeMaker("Test", [|("Field1", "string"); ("Field2", "int")|]).RecordType
printfn "IsRecordType=%b" (FSharpType.IsRecord(myType))
printfn "Record fields: %A" (FSharpType.GetRecordFields(myType))
demonstrates for a purely synthetic type `myType` the proof of concept:
IsRecordType=true
Record fields: [|System.String Field1; Int32 Field2|]
Problem
I would like to craft a simple record type based on fields provided. That is : ``` let rectype = MakeRecordType(['fieldname1'; 'fieldname2']) ``` Going directly to type providers looks like heavy gunpower for such a simple task. Are there any other way ? update I found the following question which look very similar Creating F# record through reflection