On 07/04/2012 12:58 AM, Vincent Torri wrote: > > > On Mon, 2 Jul 2012, Eric Blake wrote: > >> Not directly with a single m4_foreach_w, but it would be possible with >> other macro constructs. Note that m4 is better suited for >> comma-separated lists instead of whitespace-separated lists, > > when you say 'better suited', you mean faster ? Yes. m4_foreach_w is more or less a wrapper that converts spaces into commas, then calls m4_foreach on the comma-separated result. Starting with comma-separated lists in the first place can use native m4 handling rather than having to do under-the-hood conversions. > > I ask because I used a simple macro that uses m4_foreach_w. Should I use > m4_foreach instead ? That all depends on the syntax you want your users to be aware of. There are some cases where whitespace-separated lists are easier for users to type. Furthermore, in autoconf particularly, there is a benefit to using whitespace separation when you are interacting with shell code output (for example, having the flexibility to write 'for i in $1; do', but also do m4 processing on each element of $1). In other words, the trade-off between m4 speed and ease of use is not always trivial. -- Eric Blake eblake@xxxxxxxxxx +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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