Daniel Shahaf wrote: > Gabriela Gibson wrote on Mon, Jun 10, 2013 at 23:39:45 +0100: >> On 6/10/13, Daniel Shahaf <danie...@elego.de> wrote: [...] >> >> ---------- **** ------------ >> >> >> >> + How does this parse "%%%f1%"? Is "%%f1%%" an error? >> >> >> >> %%%f1% becomes %%f1% and %%f1%% becomes %f1%%, neither is an error. >> >> >> >> However, %f1%% is parsed out as sub%, also, +%f1% ends up as +sub. >> > >> > I'm not sure I understand. I expect %%%f1% to become %sub and %f1%% to >> > be either an error or sub%. Is that what is implemented? >> >> No. We sub only %f1% where we find it, but if it's escaped with >> one or more %'s, we eat exactly one of those instead, so %%%f1% becomes >> %%f1%. > > That's not the behaviour I would expect. What I would expect is what I > mentioned in my question: that the string is parsed left-to-right, and > whenever an % is seen, the next character is either % in which case a > literal % is emitted, or 'f1%' (or one of the other five replaceables) > in which case it is replaced; if it is anything else, the behaviour is > undefined / not promised. > >> %f1%% becomes sub% as per request by Julian Foad, because some >> diff clients accept syntax like +sub and sub+ (so, you'd use >> +%f1% and %f1%+ respectively to get that). > > Okay. I would have expected '%f1%%%' were required to get 'sub%', and > leave the case of a 'foobar%' (and '%f1%%') as undefined behaviour. > > What do others think about these %-escaping issues?
There are lots of variable-substitution (or 'interpolation') schemes in the world already -- please don't invent another one. Choose an existing scheme, look up the spec on the Internet and reference it, and then implement (the relevant parts of) it. If there's a scheme that we're already using in Subversion, that would be a good choice. Is there one? If not, I don't much like the Windows '%foo%' scheme because it's rather irregular compared to others, but if that's what we want to use then I guess that's OK with me, but again, find the spec on the Internet and refer to that. - Julian
