Keep in mind that fmt!'s interface is misdesigned at the moment: with the
current interface the result is allocated on the heap even when the output is
destined for a file or the screen. This is one of the bugs that resulted in
poor performance (an order of magnitude slower than Python) on Chris Leary's
benchmark. Fixing this will probably require having something like writefln or
printfln.
Jack Moffitt <[email protected]> wrote:
>I saw https://github.com/mozilla/rust/pull/7779 come up today and
>commented on it. I got to thinking about it some, and since the bug
>doesn't seem the right place for such discussion, I wanted to bring it
>up here.
>
>The PR proposes to rename print!() and println!() to printf!() and
>printfln!(). The original macros exist to replace uses of print() and
>println() that look like: println(fmt!("blah blah %s", s));
>
>Having a good default way to print things is very important, and it's
>one of the first things people will see of the language. I think it's
>worth bikeshedding it a bit to see if we can't come up with something
>better than the status quo.
>
>I propose instead:
>
>1) Do away with the formatting stuff as the default. print!() and
>println!() should just take a variable number of arguments, and each
>one should be printed in its default string representation with a
>space between each one. This is how Clojure's (and Python's?) print
>and println work.
>
>This would change code like this: println!("The result is %f", foo);
>to this: println!("The result is", foo)
>
>It's much easier. There are no formatting codes to remember and it
>does exaclty what you want in most cases. Consider: println!(a, ,b, c,
>"d=", d); This seems great for the standard printf-style debugging.
>
>If formatting is needed, it's easy to get to:
>println!("My name is", name, "and I scored", fmt!("%0.2f", score));
>
>2) Since println!() is likely to be used the most often, I feel like
>it should have a shorter name. Ie, we should call it just print!(),
>and have a newline-less version with a different name, or perhaps a
>different style of invocation of the macro.
>
>
>As some data to ponder, I went through the Servo code and all its
>dependencies:
>
>- The dependencies of servo use println 42 times, 24 of which also use
>fmt!(). None of these need to use fmt!() at all, they could just use
>the default string representation.
>
>- Servo itself uses println about 10 times, only two of which need
>fmt!(). These two uses are both fancy formatted output for the
>profiler.
>
>Changing all these uses to print!() in the codebase (aside from the
>two profiler fmt!()s) would make things much nicer looking.
>
>jack.
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