How to cause TikZ's 'sharp/rounded corners' options to apply immediately?

Question

Consider the following LaTeX manuscript (the TikZ code is copied from the first example on p. 146 of the TikZ & PGF Manual for Version 3.0.1a):

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
  \draw (0,0) -- (1,1)
  [rounded corners] -- (2,0) -- (3,1)
  [sharp corners] -- (3,0) -- (2,1);
\end{tikzpicture}
\end{document}

Compiling this file with pdflatex produces the following pdf file:

Note that the corners don't change from sharp to round and vice versa immediately after the corresponding option is given, but rather starting with the next corner. How can I make the options apply immediately?

Answer 1

The manual version 3.0.1a Section 14 says:

At any point where TikZ expects a path operation, you can also give some graphic options, which is a list of options in brackets, such as [rounded corners]. These options can have different effects: 1. Some options take “immediate” effect and apply to all subsequent path operations on the path. For example, the rounded corners option will round all following corners, but not the corners “before” and if the sharp corners is given later on the path (in a new set of brackets), the rounding effect will end.

When you place the rounded corners option right after the first line generated, it will not use the already generated line, but the intersection of the subsequent (following) two lines which are:

Line goes from (2,0) to (3,1)

Line goes from (3,1) to (3,0)

Therefore, if you want to apply it to the first line, you need to tell Tikz about it before it is generated.