Re: [Vala] Why the temporary variables in the C code are usefull ?

[Jim Peters <jim uazu net>]

Jacques-Pascal Deplaix wrote:
> > Unwanted side effects can happen if you evaluate an expression more
> > than once, e.g. if you substituted the full expression for every
> > _tmp2_ in the C code.  Expressions with side-effects include function
> > calls and stuff which modifies variables, e.g. p++.  You don't want to
> > do 'p++' twice or call the function twice.
>
> Thanks.  I give a clearer example of what you're saying:
>
> y = x++ + --x;

No, that isn't what I meant.  Someone who knows the Vala compiler well
could probably come up with a better example, but the compiler could
in theory transform this:

  y = x++;
  z = y * y;

into this:

  z = x++ * x++;

But that would be a mistake.  You need to hold that intermediate 'y'
value somewhere to avoid doing x++ twice.  So some temporary variables
are always needed.

Jim

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