sizeof(var) vs sizeof(type), was Re: [PATCH] git: use COPY_ARRAY and MOVE_ARRAY in handle_alias()

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Hi Peff,

On Mon, 23 Sep 2019, Jeff King wrote:

> On Thu, Sep 19, 2019 at 10:48:30PM +0200, René Scharfe wrote:
>
> > Use the macro COPY_ARRAY to copy array elements and MOVE_ARRAY to do the
> > same for moving them backwards in an array with potential overlap.  The
> > result is shorter and safer, as it infers the element type automatically
> > and does a (very) basic type compatibility check for its first two
> > arguments.
> >
> > These cases were missed by Coccinelle and contrib/coccinelle/array.cocci
> > because the type of the elements is "const char *", not "char *", and
> > the rules in the semantic patch cautiously insist on the sizeof operator
> > being used on exactly the same type to avoid generating transformations
> > that introduce subtle bugs into tricky code.
>
> Another good reason to use "sizeof(var)" instead of sizeof(type)". :)

That is indeed a very good reason, in addition to getting the type right
automatically (by virtue of letting the compiler pick it).

Should we make this an explicit guideline in our documentation?

Ciao,
Dscho

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