DIP 1027--String Interpolation--Final Review Discussion Thread

[FeepingCreature]

On Wednesday, 5 February 2020 at 05:26:30 UTC, Walter Bright 
wrote:
> The reason for formatted strings is for formatting that is 
> other than the default, and to interface with common functions 
> that use formatted strings.
>
> Strings and expressions are stuck with the default format. If 
> you're happy with the default formatting,
>
>     writefln("I want $i bananas");
>
> is not much of any improvement over:
>
>     writeln("I want ",i," bananas");

I think it's still a significant improvement. In my experience, 
anything that forces you to context switch from "inside string" 
to "outside string" is a frustrating source of typos and 'mental 
hiccups'. The point of format strings is that you can "stay 
inside" the string context and open a *new* expression context 
instead of mentally pre-flattening the string tree out into a 
list of fragments. (This is also a significant weakness of mixin 
strings.)

In other words, the difference between ("I want $i bananas") and 
("I want ", i, " bananas") is that one is (I want (i) bananas) 
and the other is ((I want ), (i), ( bananas)) - going down to 
nest vs going *up* to nest.

This may sound trivial, but trivial syntax enhancements matter, 
especially for a "top-ten" feature like format strings.