thanks_chadnt.fs

open System


let f(os: Option<string>) =
  match os with Some(s) -> s.AsSpan()
                | None -> raise(Exception())
                          ReadOnlySpan.Empty

let g(os: Option<string>) =
  let s = match os with Some(s) -> s
                        | None -> raise(Exception())
  s.AsSpan()

​thanks_chadnt.il

.assembly _
{
    .custom instance void [FSharp.Core]Microsoft.FSharp.Core.FSharpInterfaceDataVersionAttribute::.ctor(int32, int32, int32) = (
        01 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00
    )
    .hash algorithm 0x00008004 // SHA1
    .ver 0:0:0:0
}

.class private auto ansi '<Module>'
    extends [System.Runtime]System.Object
{
} // end of class <Module>

.class public auto ansi abstract sealed _
    extends [System.Runtime]System.Object
{
    .custom instance void [FSharp.Core]Microsoft.FSharp.Core.CompilationMappingAttribute::.ctor(valuetype [FSharp.Core]Microsoft.FSharp.Core.SourceConstructFlags) = (
        01 00 07 00 00 00 00 00
    )
    // Methods
    .method public static 
        valuetype [System.Runtime]System.ReadOnlySpan`1<char> f (
            class [FSharp.Core]Microsoft.FSharp.Core.FSharpOption`1<string> os
        ) cil managed 
    {
        // Method begins at RVA 0x2050
        // Code size 43 (0x2b)
        .maxstack 4
        .locals init (
            [0] class [FSharp.Core]Microsoft.FSharp.Core.FSharpOption`1<string>
        )

        IL_0000: ldarg.0
        IL_0001: brtrue.s IL_0005

        IL_0003: br.s IL_0013

        IL_0005: ldarg.0
        IL_0006: stloc.0
        IL_0007: ldloc.0
        IL_0008: call instance !0 class [FSharp.Core]Microsoft.FSharp.Core.FSharpOption`1<string>::get_Value()
        IL_000d: call valuetype [System.Runtime]System.ReadOnlySpan`1<char> [System.Memory]System.MemoryExtensions::AsSpan(string)
        IL_0012: ret

        IL_0013: ldc.i4.0
        IL_0014: brfalse.s IL_001e

        IL_0016: ldnull
        IL_0017: unbox.any [FSharp.Core]Microsoft.FSharp.Core.Unit
        IL_001c: br.s IL_0024

        IL_001e: newobj instance void [System.Runtime]System.Exception::.ctor()
        IL_0023: throw

        IL_0024: pop
        IL_0025: call valuetype [System.Runtime]System.ReadOnlySpan`1<!0> valuetype [System.Runtime]System.ReadOnlySpan`1<char>::get_Empty()
        IL_002a: ret
    } // end of method _::f

    .method public static 
        valuetype [System.Runtime]System.ReadOnlySpan`1<char> g (
            class [FSharp.Core]Microsoft.FSharp.Core.FSharpOption`1<string> os
        ) cil managed 
    {
        // Method begins at RVA 0x2088
        // Code size 25 (0x19)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: brtrue.s IL_0005

        IL_0003: br.s IL_000d

        IL_0005: ldarg.0
        IL_0006: call instance !0 class [FSharp.Core]Microsoft.FSharp.Core.FSharpOption`1<string>::get_Value()
        IL_000b: br.s IL_0013

        IL_000d: newobj instance void [System.Runtime]System.Exception::.ctor()
        IL_0012: throw

        IL_0013: call valuetype [System.Runtime]System.ReadOnlySpan`1<char> [System.Memory]System.MemoryExtensions::AsSpan(string)
        IL_0018: ret
    } // end of method _::g

} // end of class _

.class private auto ansi abstract sealed '<StartupCode$_>.$_'
    extends [System.Runtime]System.Object
{
} // end of class <StartupCode$_>.$_

​​.sharplab.json

{
    "version": 1,
    "target": "IL",
    "mode": "Release",
    "branch": "core-x64"
}