documentclass{article}
usepackage{tikz,ifthen}
usetikzlibrary{calc,patterns}

defPatternArray{%
horizontal lines,%
vertical lines,%
north east lines,%
north west lines,%
grid,%
crosshatch,%
dots,%
crosshatch dots,%
fivepointed stars,%
sixpointed stars,%
bricks,%
checkerboard}

begin{document}

essai

pgfmathparse{PatternArray[0]}
pgfmathresult
end{document}