Interpolated strings

[Nick Sabalausky (Abscissa) via Digitalmars-d]

On 04/20/2017 02:28 PM, Atila Neves wrote:
>
> I don't understand how
>
> writeln($"{a} times 3 is {a * 3}");
>
> is even marginally better than
>
> writeln(a, " times 3 is ", a * 3);  // look ma, works right now!
>
> It's not even fewer characters.
>
> Atila
>

The latter IS pretty good, I use it often. It's *VASTLY* better than 
format strings[1].

But, cognitively, I find the former much easier to read and write 
(Apparently many other people seem to as well, although perhaps not 
everyone). I'm not sure I can explain why especially well, but the 
visual parsing is just much simpler and more symmetric, and it's much 
easier to tell at a glance where the full, umm "string", starts and 
ends, and what's going inside the string and what isn't.

[1] Format strings, even with the new compile-time improvements in the 
latest DMD, for one thing, they still fail at DRY: Ie, with format 
strings, even compile-time ones, you're listing your parameters TWICE - 
once to describe WHERE they go and how they're formatted, and then again 
SEPARATELY to select WHAT data to be rendered.

And then format strings also have the downside that the "WHAT data" is 
specified out-of-band, making it making it easy to get things flipped 
around, and just generally harder to see at-a-glance what's going on 
(similar to how UFCS chains can be easier to read than a tree of nested 
function calls, because for UFCS chains the ordering is perfectly 
sequential, unlike nested function calls and format strings where the 
logic jumps around).

TBH, I'm not all that excited about the compile-time enhancements to 
format strings simply because...they're still format strings. And not 
only that, but they're printf-style syntax which is a total unintuitive 
mess (C#'s format string syntax was vastly better...for a format string, 
anyway...)

IMO, the only time a format string should be used instead of 
std.conv.text() or interpolated strings is when:

1. You're just rendering *one* value at a time with non-standard 
formatting options (ie, left-/right-justified, leading/trailing zeroes, 
etc). (Speaking of which, `interp` could really use some formatting 
features so this could be avoided, and for performance reasons.)

2. You need to support custom formatting specified at runtime (ex: 
software that supports displaying date/time in custom user-defined 
formats) but want to be lazy about it and not bother finding/writing a 
more user-friendly formatting syntax than printf-style (ie, extremely rare).