DIP 1027---String Interpolation---Format Assessment

[Adam D. Ruppe]

On Thursday, 27 February 2020 at 14:32:29 UTC, Petar Kirov 
[ZombineDev] wrote:
> 2. Have the new type implicitly convert to printf-style args. I 
> think this is what Adam is proposing. While nice to have, I 
> don't think it's necessary.

You can read my document for more detail

https://github.com/dlang/DIPs/pull/186

But basically

writefln(i"hi $name, you are visitor ${%2d}(count)");

gets turned into:

writefln(
    // the format string is represented by this type
    new_type!("hi ", spec(null), ", you are visitor ", 
spec("%2d"))(),
    // then the referenced arguments are passed as a tuple
    name,
    count
)


So very, very, very similar to Walter's proposal, just instead of 
the compiler generating the format string as a plain string, the 
format string is represented by a new type, defined by the spec 
and implemented by druntime. As a result, no more guess work - it 
is clear that this is meant to be interpreted as a format string. 
It is clear which parts are placeholders/specifiers for which 
arguments.