TFS 2015 Can build variables access other build variables?

Question

When I define a custom variable in the new TFS 2015 team build as follows:
Name: SomeOutput
Value: $(System.DefaultWorkingDirectory)\Some

...it doesn't seems to expand $(System.DefaultWorkingDirectory).
Is there a way around this?

EDIT:
At least it seems it's not expanded everywhere.

For example, in MSBuild-Arguments, /p:OUTPUT="$(SomeOutput)" is expanded to /p:OUTPUT="C:\TfsData\BuildAgents\_work\3\s\Some" but when i add a cmd line build task with tool set to cmd and parameter set to /k set, it prints
SOMEOUTPUT=$(System.DefaultWorkingDirectory)\Some

EDIT 2: Here are my variables

This is my workflow step

And this is what the build prints

Answer 1

You can use the VSTS Variable Tasks extension from the Visual Studio Marketplace.

When you define a variable in the Variables screen and use other variables as value, they won't be expanded (as you may have expected). Instead the literal text is passed to the tasks in the workflow. Without this little task the following configuration won't work:

Variable              Value
Build.DropLocation    \\share\drops\$(Build.DefinitionName)\$(Build.BuildNumber)

By adding the Expand variable(s) task to the top of your workflow, it will take care of the expansion, so any task below it will receive the value you're after.

^{https://github.com/jessehouwing/vsts-variable-tasks/wiki/Expand-Variable}

PS: The new agent (version 2.x) auto-expands variables now.