Inefficient `string` function implementation

[vasily-kirichenko]

This line of code

let s = string 22

compiles to this:

object obj = 22;
if (obj != null)
{
	IFormattable formattable = obj as IFormattable;
	if (formattable != null)
	{
		IFormattable formattable2 = formattable;
		formattable2.ToString(null, (IFormatProvider)CultureInfo.InvariantCulture);
	}
	else
	{
		object obj2 = obj;
		obj2.ToString();
	}
}

1. Why check for null after boxing?
2. Why we need to ask for IFormatProvider for ints?
3. Why we need to format it with InvariantCulture?
4. Why intermediate obj2 variable?

As I understand the function is defined here https://github.com/Microsoft/visualfsharp/blob/master/src/fsharp/FSharp.Core/prim-types.fs#L4485

[<CompiledName("ToString")>]
let inline string (x: ^T) = 
        anyToString "" x
        // since we have static optimization conditionals for ints below, we need to special-case Enums.
        // This way we'll print their symbolic value, as opposed to their integral one (Eg., "A", rather than "1")
        when ^T struct = anyToString "" x
        when ^T : float      = (# "" x : float      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : float32    = (# "" x : float32    #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : int64      = (# "" x : int64      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : int32      = (# "" x : int32      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : int16      = (# "" x : int16      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : nativeint  = (# "" x : nativeint  #).ToString()
        when ^T : sbyte      = (# "" x : sbyte      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : uint64     = (# "" x : uint64     #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : uint32     = (# "" x : uint32     #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : int16      = (# "" x : int16      #).ToString("g",CultureInfo.InvariantCulture)
        when ^T : unativeint = (# "" x : unativeint #).ToString()
        when ^T : byte       = (# "" x : byte       #).ToString("g",CultureInfo.InvariantCulture)

[dsyme]

What tool are you using to get the results? I don't see where the "g" has gone.

I have to say I don't see a specific issue here that we would consider a bug unless we had a concrete perf test showing that this was problematic and improved?

p.s. Formatting with InvariantCulture is the spec for string.

[vasily-kirichenko]

I forget why I created this issue.