F# under the covers III

To date we've seen examples where some simple F# code maps to something horrid in the C# view we get from Reflector.

Now for something completely different...

Simple properties like

	[<DefaultValue(true)>]
	val mutable private points : int
	member self.Points with get() = self.points and set(v) = self.points <- v

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map quite directly from F# into IL, even in debug build

	.method public specialname instance void set_Points(int32 v) cil managed
	{
	.maxstack 4
	L_0000: nop
	L_0001: ldarg.0
	L_0002: ldarg.1
	L_0003: stfld int32 Tinesware.InfrastructureTests.CoverageExemptionTest::points
	L_0008: ret
	}
	.method public specialname instance int32 get_Points() cil managed
	{
	.maxstack 3
	L_0000: nop
	L_0001: ldarg.0
	L_0002: ldfld int32 Tinesware.InfrastructureTests.CoverageExemptionTest::points
	L_0007: ret
	}

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where set_Points just assigns straight into the field, and get_Points just returns it, roughly as expected.

The corresponding C#

	private int points;
	public int Points { get { return points; } set { points = value; } }

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becomes

	.method public hidebysig specialname instance void set_Points(int32 'value') cil managed
	{
	.maxstack 8
	L_0000: nop
	L_0001: ldarg.0
	L_0002: ldarg.1
	L_0003: stfld int32 Tinesware.TestData.Class1::points
	L_0008: ret
	}
	.method public hidebysig specialname instance int32 get_Points() cil managed
	{
	.maxstack 1
	.locals init (
	[0] int32 CS$1$0000)
	L_0000: nop
	L_0001: ldarg.0
	L_0002: ldfld int32 Tinesware.TestData.Class1::points
	L_0007: stloc.0
	L_0008: br.s L_000a
	L_000a: ldloc.0
	L_000b: ret
	}

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The set_Points code is the same, modulo the maxstack -- but what are that temporary and that branch doing in get_Points?

This is a bit of a "lolwut!?" discovery!

Reassuringly, the release build of the C# get_Points is almost a nop-free version of the F# debug code

	.method public hidebysig specialname instance int32 get_Points() cil managed
	{
	.maxstack 8
	L_0000: ldarg.0
	L_0001: ldfld int32 Tinesware.TestData.Class1::points
	L_0006: ret
	}

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but as the debug version is the one for doing code analysis on, that's less useful.

This is unchanged with the Feb 2010 CTP (1.9.9.9).