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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