Thursday, November 26, 2009

F# under the covers XI -- Literal expressions that aren't; attributes that don't

The problem with being unable to attribute just the getter or setter of a property is resolved at the release (February 2010 CTP).

Consider the following simple C# property

This compiles in debug mode to

which assigns the literal result -- 6 -- of the expression to the temporary that is then returned. The analogous F# method

compiles to IL which preserves the expression to execute only at run time:

which makes static analysis of the code in the more usually analysed state a rather more complicated business.

Another complicating factor is that while this syntax

builds, it attaches the attribute (with Method and Constructor usage only) to the property as a whole; and not the generated get_Options method, as in

What I'd like to express, and what I've not found a way to express, is

and MSDN remains opaque on the subject as well.

This is something I could code around, but I can't yet see a clean way of doing to allow separate attributes on the getters and the setters.

Later: The intended syntax for this option is, much as you might expect, this:

with the necessary insets as shown (to avoid error FS0010: Incomplete structured construct at or before this point in pattern), however on filing a bug report I got confirmation that it is a known issue with the Beta 2 release (aka October 2009 CTP), that this still decorates the property and not just the getter.


Anonymous said...

Doesn't this work as expected ?

static member Options with
  [< CoverageExemption( Points = 1, Justification = "Code generated is not a Literal") >]get() =
     System.IO.FileShare.Write ||| System.IO.FileShare.Delete

Steve Gilham said...
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