To also clarify on why @sprintf behaves this way, the reason is that it compiles down to specialised code for printing e.g. a float, followed by a double, etc., whatever you specify. If you use a variable like `fmt` the actual value is only available long after the code has already been compiled.
This could certainly be supported this by falling back to interpreting the string at runtime, if necessary – the code just hasn't been written yet. Another workaround is to call eval(:@sprintf($fmt, 29)). This will probably be fairly slow, though. I have another solution which will help with repeated format strings, but will need to send a PR to base to get that working. On 3 December 2014 at 01:58, John Myles White <johnmyleswh...@gmail.com> wrote: > I think both of the problems you're hitting are the same core problem: > @sprintf is a macro, so its behavior is surprising when you think in terms > of the run-time behaviors that control function evaluation. In particular, > your line continuation problem wouldn't be fixed by having line > continuations. No matter what you're going to end up passing the wrong > thing (a call to *) to a macro that expects a literal string. > > I believe Dahua tried to work on writing a more function oriented package > for doing formatting: https://github.com/lindahua/Formatting.jl > > There might be some other solutions floating around as well. > > -- John > > On Dec 2, 2014, at 5:52 PM, Ronald L. Rivest <rivest....@gmail.com> wrote: > > Another reason for (perhaps) wanting an expression as a format > string: > > Julia doesn't have a line continuation mechanism. > > How does one split a long format string into parts without having > a string expression? The following doesn't work: > > @sprintf("This is the first part of a rather long format string, which > I" * > "would like to extend onto %d (or maybe more) lines.", > 5) > > Thanks. > > Cheers, > Ron > > > On Tuesday, December 2, 2014 8:40:56 PM UTC-5, Ronald L. Rivest wrote: >> >> I'm new to Julia, and got burned (aka wasted a fair amount of time) >> trying to sort out why @sprintf didn't work as I expected. >> >> julia> @sprintf("%2d",29) >> "29" >> >> julia> fmt = "%2d" >> "%2d" >> >> julia> @sprintf(fmt,29) >> ERROR: @sprintf: first argument must be a format string >> >> julia> @sprintf("%"*"2d",29) >> ERROR: @sprintf: first argument must be a format string >> >> I would expect that @sprintf would allow an arbitrary string expression >> as its >> format string. It obviously doesn't... >> >> There are many good reasons why one might want a format string expression >> instead >> of just a constant format string. For example, the same format may be >> needed in >> several places in the code, or you may want to compute the format string >> based on >> certain item widths or other alignment needs. >> >> At a minimum, this should (please!) be noted in the documentation. >> >> Better would be to have the extended functionality... >> >> (Or maybe it exists already -- have I missed something?) >> >> Thanks! >> >> Cheers, >> Ron Rivest >> > >
