Add built-in First and Last item functions

[kzu]

Sometimes it's useful to take just the first item on a list, or the last. This is currently very cumbersome, to the point that it's "easier" just write an inline task to do so.

A new First() and Last() item function would simplify things a lot.

Usage example:

   <Target Name="Split">
        <ItemGroup>
            <BranchParts Include="release;v1.3.1" />
        </ItemGroup>

        <Message Text="@(BranchParts -> Last())" Importance="high" />
        <Message Text="@(BranchParts -> First())" Importance="high" />
    </Target>

Renders:

v1.3.0
release

[Rabadash8820]

I just bumped into this challenge myself, and came across the exact same inline task article 😄 My use case is parsing a version string from a file with the ReadLinesFromFile task. The exact format of the file is beyond my control (a Unity3D ProjectVersion.txt file), but I know that the first line of the file is in the format m_EditorVersion: <version>. ReadLinesFromFile returns the file lines as an item collection, so I'd like to be able to call First in some way.

[jrdodds]

With First() (or Car()) there should be a Cdr() equivalent function added as well.

For a list of 1;2;3, First() would return 1 and Cdr() would return 2;3.

(Car and cdr are from Lisp and cdr is clearly not a good name for this function in MSBuild.)

[KalleOlaviNiemitalo]

Could call the CDR feature @(Itemtype->Skip(1)), similar to System.Linq.Enumerable.Skip.

[jrdodds]

Yes. Modeled on System.Linq.Enumerable, there could be First(), Last(), Skip(n), and Take(n).