Calling op_Addition on primitive types doesn't work

[gusty]

Calling op_Addition on primitive types doesn't work but works on new BCL types.

Repro steps

> System.Int32.op_Addition (3, 6) ;;

  System.Int32.op_Addition (3, 6) ;;
  -------------^^^^^^^^^^^

C:\Repos\stdin(3,14): error FS0039: The type 'Int32' does not define the field, constructor or member '+'.

but

> System.Int128.op_Addition (3, 6) ;;
val it: System.Int128 = 9

Expected behavior

Same in both cases

Actual behavior

The former doesn't work, the latter does.

Known workarounds

Don't do it.

Related information

In case this is somehow expected we need to document this in the RFC.
Also I wonder if the definition of standard F# operators is adapted in order to work on new BCL interfaces like IAdditionOperators, it seems they are not, which means if I define my own type implementing IAdditionOperators I won't be able to just use F# standard + operator, without having to redefine it. The RFC doesn't mention about adjusting existing math operators, maybe it should clarify.

Microsoft (R) F# Interactive version 12.0.5.0 for F# 7.0

Microsoft Visual Studio Community 2022 (64-bit) - Preview
Version 17.4.0 Preview 2.1

[vzarytovskii]

There's difference of how operators are defined on both types:
https://github.com/dotnet/runtime/blob/200f533e063a470514c6bd95e5d4c6fcc5d97266/src/libraries/System.Private.CoreLib/src/System/Int32.cs#L300-L301, here explicit interface member is implemented:

/// <inheritdoc cref="IAdditionOperators{TSelf, TOther, TResult}.op_Addition(TSelf, TOther)" />
static int IAdditionOperators<int, int, int>.operator +(int left, int right) => left + right;

https://github.com/dotnet/runtime/blob/200f533e063a470514c6bd95e5d4c6fcc5d97266/src/libraries/System.Private.CoreLib/src/System/Int128.cs#L709-L719, and here operator is defined on type:

public static Int128 operator +(Int128 left, Int128 right)
{
    // Implementation
}

So, I'd say it's expected.