save optional parameter of command

Question

I want to have a command that by default uses a default string and if supplied the optional parameter. I tried it using let, but that gives strange results

\documentclass{minimal}

\newcommand{\standardstring}{standard}
\newcommand{\printresult}[1][\standardstring]{%
    \let\printstring#1
    \printstring
}

\begin{document}   
\printresult

\printresult[abc]
\end{document}

This results in

standard
bc a

Answer 1

In the first case, the assignment is:

\let\printstring\standardstring␣

The non-standard case:

\let\printstring abc␣

In both cases the line contains a space by the end of line. In the latter case the assignment is \let\printstring=a. Then bc and the space from the end of line is set, finally \printstring follows.

Perhaps you want something like:

\documentclass{minimal}

\newcommand{\standardstring}{standard}
\newcommand{\printresult}[1][\standardstring]{%
    \def\printstring{#1}%
    \printstring
}

\begin{document}
\printresult

\printresult[abc]
\end{document}

Answer 2

\documentclass{minimal}
\newcommand\standardstring{standard}
\newcommand{\printresult}[1][\standardstring]{%
  \edef\standardstring{#1}#1}

\begin{document}   
\printresult

\printresult[abc]

\printresult
\end{document}