startsWith using an array of needles

[H. S. Teoh]

On Tue, Aug 20, 2013 at 03:16:28PM -0400, Jonathan M Davis wrote:
> On Tuesday, August 20, 2013 19:14:08 Byron wrote:
> > On Tuesday, 20 August 2013 at 16:51:35 UTC, Jonathan M Davis
> > 
> > wrote:
> > > On Tuesday, August 20, 2013 17:58:19 Byron wrote:
> > >> I am trying to use startsWith with an array of needles. Failes
> > >> with not being able to match any functions. Not sure if there is
> > >> a work around.
> > >> 
> > >> const auto ignore = [".git/", ".gitignore"];
> > >> 
> > >> foreach(DirEntry e; getcwd.dirEntries(SpanMode.depth).filter!(a
> > >> => !a.name.startsWith(ignore))) {
> > >> writeln(e.name);
> > >> }
> > > 
> > > startsWith dosen't take an array of needles. It takes a variadic
> > > list of them.  So, it needs to be something more like
> > > 
> > > !a.name.startsWith(".git/", ".gitignore")
> > > 
> > > If you want to save the list though, you can use
> > > std.typetuple.TypeTuple and
> > > an alias:
> > > 
> > > alias TypeTuple!(".git/", ".gitignore") ignore;
> > > 
> > > At that point, the rest of your code should work as-is.
> > > 
> > > - Jonathan M Davis
> > 
> > What if I want to load my ignore list from a file?
> 
> Then you'll have to make separate calls to startsWith. The number of
> arguments has to be known at compile time, so unless the number of
> arguments from the file is always the same, and you have a variable
> per argument, you can't do it.  But unless the needles have similar
> prefixes, there isn't going to be much of an efficiency hit from
> multiple calls.
[...]

And if you're worried about efficiency, I suggest constructing and
caching a regex for doing the matching. It will be better than a long
series of startsWith calls if your ignore list is large.


T

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