The state of string interpolation

[H. S. Teoh]

On Fri, Dec 07, 2018 at 05:11:35PM +0000, Atila Neves via Digitalmars-d wrote:
[...]
> Every language change is a cost, and therefore should justify its
> inclusion.  I personally don't think that it is in this case just to
> make a niche use case slightly easier, and this coming from someone
> from that niche! From now on it's:
> 
> const code = mixin(interp!q{
>     // stuff that I used to write with many %s and it was hard to match them
> up
> });

One thing I like about format() that string interpolation doesn't
(easily) give, is the ability to specify additional formatting
parameters, e.g., %6.2f, or %04X. You'd have to basically "uglify"
string interpolation in much the same ways in order to get equivalent
functionality, e.g., (hypothetical syntax) "Price is ${6.2:price}.".

The one thing missing from format(), as you point out above, is the lack
of named arguments for long format strings.  This could be fixed by
extending format() with named placeholders, so that you can do something
like:

	// Hypothetical syntax
	format(q"CODETEMPLATE
		void %{funcName}s(%{funcParams}(%s, %)) {
			%{boilerPlate}s
			for (i; 0 .. %{numIter}d)
			{
				%{loopBody}s
			}
		}
	CODETEMPLATE", NamedArgs([
		"funcName", "myFunc",
		"funcParams", ["int x", "float y", "string z"],
		"boilerPlate", generateBoilerplate(),
		"loopBody", generateFuncBody(),
		"numIter", 255
	]));

Basically, instead of sequential arguments (or numerically-indexed
arguments like $#1), format takes what amounts to a polymorphic
associative array from which it can look up named arguments. This gets
rid of the "too many %s I can't figure out which argument is which"
problem, plus it makes your format string more readable and
maintainable. It allows the same argument to be referenced multiple
times, and arguments don't have to appear in the order they appear in
the format string (important for i18n uses).

Note that NamedArgs can be dispensed with if the language supported
named arguments (like in Python, `myfunc(width = 123, height = 234)`).


T

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