[Issue 7019] implicit constructors are inconsistently allowed

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=7019

--- Comment #16 from Denis Shelomovskij <verylonglogin.reg at gmail.com> ---
(In reply to Kenji Hara from comment #15)
> (In reply to Denis Shelomovskij from comment #14)
> > static assert(!__traits(compiles, { S2 s2 = { 5 }; })); // fails
> > static assert(!__traits(compiles, { S2 s2 = { s: 5 }; })); // fails
> 
> These are expected behavior.
> The target type of the argument '5' can be determined to S, so implicit
> constructor call is handled.

How does `S2 s2 = { 5 }` differ from `f(5)` or `S2 s2 = S2(5)`? IMO the only
clean rule is:

  "Implicit conversion exists iff target type is explicitly stated."

What is wrong with this rule? What rules and why are preferred?

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